Conn: I'm Ariel Conn with the Future of Life Institute. With April hosting Earth Day, the March for Science, and the People's Climate March, it seemed like a natural month to focus on climate change for our podcast. I'm also a resident of Boulder, Colorado, which means today I have the opportunity and honor to sit in the offices of the National Center for Atmospheric Research with climate scientists, Kevin Trenberth and Brian Toon.

Dr. Trenberth is a distinguished senior scientist in the Climate Analysis Section at the National Center for Atmospheric Research (NCAR), where he studies climate variability and change. He has been prominent in most of the Intergovernmental Panel on Climate Change (IPCC) Scientific Assessments of Climate Change, and one of the most cited scientists in his field.

Dr. Toon is a professor in the Department of Atmospheric and Ocean Sciences at the University of Colorado in Boulder, Colorado. He has investigated the climate changes that killed the dinosaurs, climate changes after large volcanic eruptions, climate changes that follow a nuclear war, as well as the distant past and far future climates of Earth. Dr. Trenberth and Dr. Toon, thank you so much for joining us today.

Trenberth: You're most welcome.

Toon: Yeah.

Conn: So now, I'm going on the assumption that most of our audience is already convinced that climate change is real and it's a result of human activity, but even among those of us who are believers, so to speak, there seems to be groups who think the future is in bad shape and others who recognize climate change poses risks, but think that we can address those risks in time. Dr. Trenberth, I wanted to start with you. Can you talk a little about what the current consensus is among scientists about climate change and what aspects of the research are still up in the air?

Trenberth: Well firstly, the main source of human-induced climate change is from increasing carbon dioxide and other greenhouse gases in the atmosphere. But carbon dioxide, in particular, comes from burning of fossil fuels. And so this relates directly to human activities, and we have plenty of evidence that we're responsible for the over 40% increase in carbon dioxide concentrations in the atmosphere since preindustrial times, and more than half of that has occurred since 1980.

So there is a change in the composition of the atmosphere. The US is most responsible for the largest amount of that, but, at the moment, China is putting more carbon dioxide into the atmosphere than any other country.

Now, going along with that, there are increases in the global mean surface temperature that are directly related to the increases in carbon dioxide. We can show that using climate models that we developed here at NCAR that you cannot actually get the changes that are occurring unless you include the changes in the composition of the atmosphere. Then there are all other sorts of climate change, the more complicated aspects, and the ones which affect us on a day-to-day basis, like heavy rainstorms, droughts, wildfires, heat waves, and so on, that are increasing around the world that are related to climate change. And that's a big conversation.

Conn: Okay. And Dr. Toon, did you have anything you want to add?

Toon: I think the problem is that carbon dioxide is rising proportional to population on the Earth. If you just plot carbon dioxide in the last few decades versus global population, it tracks almost exactly, so that increasing efficiencies are being offset by the expanding communities in China and third world countries using more energy. So it's not just population, but other things are balancing each other.

The problem is that, in coming decades, we're increasing global population by a million people a week. That's a new city in the world of a million people every week somewhere, and the amount of energy that's already committed to supporting this increasing population in terms of building new buildings, building new cities, putting in new streets, building new vehicles, and so on, is very large.

This is actually a very difficult situation here because the committed energy in the next two decades that supports this increasing population pretty much uses up all the leeway we have to prevent climate change of a serious magnitude. We don't really have time here to stall around with people doing things that don't make sense, like supporting coal or coal miners.

The number of coal miners in the United States, apparently, is about the same as the number workers at Arby's. I feel concerned about those people, and they should be given new training and education and something that they can do in the future, but trying to retroactively support a failing industry, which causes many other pollution problems besides just carbon dioxide, to support a small number of people, just doesn't make sense.

Conn: Okay, so how do you see us solving this? I mean, is it solvable?

Trenberth: Well, climate change is happening and it’s projected to get worse as we go into the future. And we already have considerable evidence that there are major effects around the world. In the US, I reckon it's costing us more than $10 billion a year. It's a considerable amount.

It's very uneven as to who gets affected. The big flooding events that occur are a bit erratic as to where they occur. The fact that we have flooding events is not unusual, but they're getting larger in magnitude. It's the natural variability of the weather and El Niño and so on that determines where these things occur, but the fact that they occur and they're getting bigger is related to the climate change aspect.

What we need to do about this is, firstly, recognize that it's happening and plan for the consequences if we can. This relates to what is often called adaptation and building resilience and so on.

Then, secondly, we want to slow this down and, if possible, stop the climate change if we can, but there's a tremendous amount of inertia in our system, which means we're going to have to live with a certain amount of climate change no matter what we do. But the sooner we get into this and really seriously take this on in the US and around the world, the better we will be in the future, and especially for the future generations. This relates to conservation, building more energy efficiency, switching to renewables, and all of those sort of things.

Conn: Real quick, when you say $10 billion a year, is that to, say, pay for things like recovery after a flood, or is that other costs? Do we expect those costs to be going up?

Trenberth: 2012 was the warmest year on record in the United States. There was a very widespread drought that occurred, starting here in Colorado, in the West. There were a number of wildfires up along the front range down near Colorado Springs and up near Fort Collins, and even not that far away from here in Boulder. There are costs associated with those kind of things. The drought itself was estimated to cost about $75 billion.

Superstorm Sandy is a different example. 2012, Superstorm Sandy came into the East Coast and the damages associated with that are, again, estimated to be about $75 billion. The storm is estimated to be more intense because of higher sea temperatures, and more fuel for the storm. Sea level is higher because of global climate change. It's very likely that all of the subway tunnels and the tunnels to New Jersey, to Hoboken, and to Brooklyn would not have flooded if it hadn't been for climate change. So immediately, the cost is probably about $30 billion or $40 billion that you can ascribe to climate change right there.

Then there are all of these other events that we've had in the last year: the flooding in Houston, the major flooding in Louisiana, all of the flooding associated with Hurricane Matthew along the East Coast. All of these had what were at the time regarded as thousand-year events, but they're not thousand-year events anymore. Because of climate change, they're much worse than they otherwise would have been, and the extra damage associated with that can easily run into billions of dollars. At the moment, the cost of climate and weather related disasters is something like $40 billion a year. The $10 billion a year is only a fraction of that, which is the part that's making things worse. That's where that accounting comes from.

Conn: Okay. And Dr. Toon, what are your thoughts on whether or not we can solve this and, if so, how?

Toon: It's a difficult problem because of the inertia in the system. Technologically, of course, there are lots of things we can do. Solar energy and wind energy are both approaching or passing the cost of fossil fuels, so they're advantageous. There's money to be made in promoting things like especially solar energy around the world. There's lots of countries that don't have coal, particularly in Africa and places like that, that can benefit from solar energy. Somebody's going to be selling that to them.

So there are benefits that are sort of co-benefits of solving the climate problem that are economic, and there's very little benefit to dragging our feet and trying to prevent progress in those things. There's a lot of hopeful signs that we can convert a lot of our economy and our energy to things that are not so harmful to the environment.

There's other aspects of this like air pollution, for example, which comes from burning a lot of fossil fuels. It's been estimated to kill seven million people a year around the Earth. Particularly in countries like China, it's thought to be killing about a million people a year. Even in the United States, it's causing probably 10,000 or more deaths a year. That is something that when you switch over to fuels that are not so harmful to the environment as a fossil fuel burning is, that you can gain benefits from that as well.

There are lots of technological solutions here that can improve things, but it is a race. It's a race to how fast we can convert the economy to something that's not so harmful against the growing problems caused by the warming Earth. The warming Earth is not linearly increasing. It's something that can grow exponentially, which is like investing in the stock market. You could become well off in your retirement if you just invested through your lifetime in that, and carbon dioxide works the same way. It's something that one has to be careful of that it doesn't start increasing very rapidly and having some effect, which may not be due directly to the carbon dioxide, they’re indirect links, like melting ice sheets that were thought to take a very long time to melt, but some parts of them might be vulnerable and melt more readily than we expect, which could cause very large problems to society if we just allow things to go unchecked.

Trenberth: I should just say that there's a lot of things already happening, of course, and a lot of these transitions are already occurring. But it does relate, in part, to incentives. This is where there are far too many incentives for fossil fuels at the moment. One way you can help is by providing various kinds of incentives for renewable energy. This is where things seem to be potentially stalling in the US at the moment, in the US government, so this is a bit of a worry.

Conn: So that, and what Dr. Toon was talking about with the race, brings up a question that I have. It seems like the more research that comes out, the worse the situation is. Is that the case, or I don't know if it's getting worse or if our understanding of it seems to make it worse, or is that just how the media's portraying it?

Trenberth: I don't think it really is getting worse. It's getting more refined. We can pin a lot of things down a lot more and put real numbers on them. Climate change continues to happen, but in actual fact a lot of what is happening has been projected for 20 years or more. This is not really a new problem in that regard.

Toon: There's a lot of things that we have only been able to measure recently. It's quite difficult to make measurements of the deep ocean. Most of the excess energy that the Earth is gaining is going into the ocean. People have only been making those sorts of measurements for a few decades; a very short record there.

Likewise satellite images of the poles, and looking at the detailed ice balance there in the poles is something we've only been able to do for a short period of time. Those are areas where people thought there would be problems, but they didn't really have enough of a database to tell what was happening. To that extent, things seem like perhaps they're worse because we can tell if they're changing.

Trenberth: And the ocean is a very good example because there's been a development of autonomous floats. These are remarkable devices that are deployed and they go down and reside in the ocean at about a thousand meters below the surface. Then about every week or so, they pop up to the surface, and on the way they make measurements of temperature and salinity. Then they telemeter that information back to satellites.

There are about three and half thousand of these devices populating the oceans and making measurements in places that we've never had them before, but it's really only been doing this on a global basis since about 2005. So we only have about 10 years of really good records, but it's teaching us a lot about how the oceans work, and it's enabling us to reconstruct a lot more what happened in the ocean in the past, given this information.

What we find, indeed, is that the oceans are warming. They're warming a little bit more than we previously thought. 92% of the energy imbalance from the increasing blanket of carbon dioxide that we put in the atmosphere is going into the ocean. As a result, the ocean is expanding. This means sea level is rising and, of course, the ocean is also rising because of melting of glaciers and land ice in Greenland and so on that puts more water into the ocean.

Sea level measurements are another component that we have really only had global measurements since 1992, when new satellites went into space that were making measurements to millimeter accuracy using altimeters on spacecraft. Since then, sea level has gone up by about 3.25 inches – global sea level. This is a rate of about 15 inches per century at the current time, and that's expected to increase. Rising sea level is, of course, one of the big problems in coastal regions.

Conn: Then what about things where I'm reading more about permafrost potentially being an issue releasing methane?

Trenberth: This relates to the carbon cycle. Perhaps one of the best examples relates to a compost heap. Many people have a compost heap in their yard to get rid of vegetation matter that is waste. If you have a healthy compost heap, there's a bacterial action, which breaks down the vegetation matter quite rapidly, and it puts out carbon dioxide into the atmosphere.

But if it gets very wet and slimy, it puts methane into the atmosphere, it’s a much slower process, but this is what happens in bogs around the world, where water plays a role. And it happens in areas where the ground is frozen. There's a tremendous amount of vegetation matter – carbon of various sorts – in soils and in the permafrost. As that thaws, the bacterial action starts to pick up, and it often generates methane. You may have seen examples where people in the permafrost regions, they poke a hole in the ground and then light it, and suddenly there's a burst of flame from the methane that occurs. It can be spectacular. And so as the permafrost thaws more and more, more of this methane gets into the atmosphere.

Methane is a very powerful greenhouse gas. It's about 30 times more powerful per molecule of carbon dioxide, but it has a shorter lifetime, and after about 10 years, it eventually gets oxidized and ends up as carbon dioxide. So it still contributes to the overall problem even at that point, and carbon dioxide has a really long lifetime. These kinds of changes in the climate and the changes in permafrost can feed back and amplify the original changes that we're producing from the burning of fossil fuels by adding to the composition of the atmosphere changes.

Toon: I think Kevin mentioned an important point here, which is that carbon dioxide has a very, very long lifetime. Early IPCC reports would often say carbon dioxide has a lifetime of 50 years. To some people, they interpret that to mean it'll go away in 50 years, but what it really meant was that it would go into equilibrium with the oceans in about 50 years.

The actual removal of carbon dioxide from the system – when it goes into equilibrium with the oceans it's still increased in the atmosphere – to get it out of the system, you actually have to convert it into limestones, like the White Cliffs of Dover. This has been going on over geologic history of the Earth, there's vast reservoirs of limestone on the planet that represent all this buried carbon dioxide, but the time to do that is very, very long. It's perhaps 100,000 years to convert the CO2 in the atmosphere into limestones.

When you go somewhere,    in your car, for example, when I drive back down the hill, about 20% of that carbon dioxide that is released to the atmosphere is still going to be there in thousands of years.

We're doing something for the first time on the Earth on a geologic timescale here. It's not something that we can reverse easily because we can't get it back out of the atmosphere in any way we know at the moment. It's something that's going to stay there for a longer time period than the entire history of humans on the planet.

That's a very serious thing when you do something to the environment like that. We've done this before with, for example, the ozone hole. We were using chemicals in spray cans and to blow foam and to run refrigerators and things like that that had a lifetime of about 100 years. Because it has a long lifetime, it accumulates in the atmosphere and it built up until it started to destroy the ozone layer, so then we stop producing it. The ozone hole is still there, it hasn't gone away; maybe it's showing signs it's starting to go away. And that's something with 100-year lifetime, but the CO2 has got lifetimes of thousands and thousands of years, maybe tens or hundreds of thousands of years. It's not reversible. We're doing something that's slowly and insidiously increasing, and we can't wait around for it to do something devastating to the planet because it won't be reversible. We have to anticipate what it might do and stop it before it can get to that point.

Conn: Do you see indications that we can either use existing or develop new technologies to either capture carbon or minimize our energy use?

Trenberth: Well, Mother Nature plays a role. I mean there is quite a lot of cycling of carbon dioxide through the system on an annual basis. Every springtime, the trees take up carbon dioxide and there’s a draw-down of carbon dioxide in the atmosphere, but then, in the fall, the leaves fall on the forest floor and the twigs and branches and so on, and they decay and they put carbon dioxide back into the atmosphere.

People talk about growing more trees, which can certainly take carbon dioxide out of the atmosphere to some extent, but then what do you do with all the trees? That's part of the issue. Maybe you can bury some of them somewhere, but it's very difficult. It's not a full solution to the problem.

That's one aspect of the way in which this can be dealt with. There are maybe other ways where we can try to address some aspects of climate change, but a lot of those are bandage approaches. These are approaches that are referred to as geoengineering, where we maybe try to emulate a volcano that puts a lot of debris or sulfate into the stratosphere and form small particles that block the sun, and so it cools down the planet a little bit. The difficulty with that is it deals with the incoming radiation, whereas the greenhouse problem is dealing with the outgoing longwave radiation and, in between, is the whole of the weather systems and the water cycle. There are potential side effects from fiddling with the incoming radiation versus dealing with the problem of the buildup of carbon dioxide. Those are some of the sorts of things that are talked about as maybe aspects that might play a role.

Conn: Dr. Toon, did you want to add anything?

Toon: I think it's important to know that carbon dioxide isn't just a problem because it warms the Earth up, it's also a problem because when it comes into balance with the oceans, it acidifies the ocean surface waters. This is a problem for lots of organisms that are used to the pH that the ocean is at now.

Things like coral bleaching are caused just because the temperature is warming up a little bit. And that's a problem already in the Great Barrier Reef, they're getting extensive bleaching there. The coral reef systems all through the tropics in the world, many people depend on that ecosystem for fishing, and a lot of the oceanic fish have part of their life cycle in a reef system. Those are very abundant living organisms there. They're first affected by the temperature, but a lot of the organisms are going to be affected by the acidification of the oceans as well.

That's a problem with a lot of the geoengineering schemes is that, for example, if you try to make a human volcano and cut down the solar energy, as Kevin just mentioned, you won't solve this problem of ocean acidification. Of course, if you bury the carbon then you would solve it, but people, for example, the average American uses the equivalent of about five tons of carbon a year – that's an elephant or two. That means every year you have to go out in your backyard and bury an elephant or two. There's a little bit of a volume problem there in getting rid of all the CO2.

It's non-trivial to bury it. You can't just put it into another form. Lots of people want to take the CO2 from a power plant and grow algae. That would certainly sequester the CO2 for a little while, but then you've got the algae there. It'll just decay and release the CO2 back, so you haven't really accomplished anything that way. You've got all those elephants you've got to bury every year.

Conn: If we continue at our current pace, what happens to us in the next 10 years, 50 years, 100 years?

Toon: I think there are concerns that in the near term the Earth is going to be quite a bit like it is now. I've been living in Boulder here for about 20 years. Of course, you're often tricked into thinking things have changed just because of your limited experience, but, nevertheless, I've seen it snow every month at my house in Boulder, except for August. It no longer seems to be snowing in May or June or September here. Perhaps it's just an accident, but it seems to me I can see a definite pattern there.

You expect that it will become more obvious to people as time goes on, but if we look at the more distant future, 100 years from now or so, there are parts of the Earth now that are already marginal for living in just because they're so hot. People lose heat from their bodies by sweating and things like that. It can be so hot that in certain places in the Middle East, for example, that it may not be habitable in 100 years or some time frame like that.

Of course, if we wait a thousand years, and we continue to keep pumping CO2 into the system, almost certainly we're going to put the polar caps on an irreversible melting, which will raise sea levels about 300 feet. I don't think that's survivable to many coastal cities to have a 300-foot rise in sea level.

That's a typical Earth condition. Usually the Earth does not have polar caps, and the oceans are about 300 feet deeper. The Earth is perfectly happy to have that configuration of no polar caps and a lot deeper ocean. We have to recognize we're in a special climate and environment that humans have evolved in and are used to, and that's not the typical Earth environment. Earth doesn't care what we want. It's going to do whatever it's going to do. If we push it off into a warm environment, then that will be something we'll have to deal with.

Trenberth: The key issue here is not that climate change hasn't happened in the past and isn't expected to happen in the future, but the rates of climate change that are occurring now are a factor of a hundred times faster than they have occurred over geological times. Internationally, there is an agreed upon number that when the global mean temperature has increased by about two degrees Celsius relative to preindustrial levels – and we're already at 1.1 degrees Celsius above preindustrial levels – then that creates a whole lot of extremely undesirable aspects to the climate system.

This could well occur at the current rate by around about 2060. By then, carbon dioxide will have doubled from preindustrial levels, and the consequences are that this becomes extremely disruptive for ecosystems in particular. Many of the farms that currently exist will no longer be able to farm the same crops that they now farm, at that time. Forests that now grow in various places, the trees will no longer be viable where they currently can grow.

It doesn't mean that other species, other kinds of trees will not be able to grow in those locations, but the process of moving out or getting rid of one ecosystem and then bringing in another is extraordinarily disruptive. And the rate of disruption that begins to occur in the mid-century, 2050-2060 time frame at the current rates of climate change could be extraordinarily disruptive and very, very damaging for our ability to grow enough food and supply enough water to all of the population that needs it.

The strife that occurs around the world as a consequence of this is likely to be quite uneven, but it is apt to cause more strife and it's likely to cause more conflicts, regional wars, or maybe even larger-scale wars. Potentially, this is the way in which some of the society may well break down as a consequence of these kinds of developments.

You don't actually have to go a hundred years or a thousand years into the future before things can get quite disrupted relative to today. You can see some signs of that maybe if you look around the world now. There's certainly studies that have suggested that the changes in climate, and the droughts that occur and the wildfires and so on are already extra stressors on the system and have exacerbated wars in Sudan and in Syria. In the Middle East, access to water is a key issue.

While it may not have been the dominant component, it is still a component. It’s one of the things, which makes it very worrying for security around the world to the defense department, to the armed services, who are very concerned about the destabilizing effects of climate change around the world.

Conn: This idea of the threat multipliers that you've been talking about also takes me to the opposite end of the extreme that I wanted to mention, what we think of as the other climate change, which would be nuclear winter as a result of nuclear war. Dr. Toon, can you talk a little bit about that?

Toon: Nuclear winter is caused by burning cities. If there were a nuclear war in which cities were attacked then the smoke that's released from all those fires can go into the stratosphere and create a veil of soot particles in the upper atmosphere, which are very good at absorbing sunlight. It's sort of like geoengineering in that sense; it reduces the temperature of the planet.

We've estimated if there were a war between the United States and Russia, and the number of weapons we currently have exploded in cities in the United States and Russia, and possibly in Europe or China, that the Earth would probably drop to ice age conditions in a year. Those would persist for some time and basically stop agriculture in mid-latitudes for several years, possibly as long as a decade or more.

Even a little war between India and Pakistan, for example, which, incidentally, have about 400 nuclear weapons between them at the moment. If they started attacking each other's cities, the smoke from that could drop the temperature of the Earth back to preindustrial conditions. In fact, lower than anything we've seen in the climate record since the end of the last ice age, which would be devastating to mid-latitude agriculture.

This is an issue people don't really understand. People in the western world have heard the biblical stories about storing grain for seven years and rescuing the Egyptians, but actually the world food storage is only about 60 days. There's not enough food on that planet to feed the population for more than 60 days.

In the average city, there's only enough food in an average city to feed the city for about a week. You can see that this happens if there's a snowstorm somewhere and the city gets snowed in and you can't bring any food in, then they'll start running out of food in all the supermarkets, or if there's a hurricane coming through, the same thing happens.

The world is very interdependent now, and it has a very little food on hand. It uses transportation to feed people and it uses transportation to make up for a drought in some place. If wheat stops growing in Russia, then the rest of the world will send wheat to Russia. Those sorts of things are big problems after a nuclear conflict because the whole Earth is affected. You can't ship food to some other place because everybody has lost the ability to produce food, so people start starving to death.

That's the same kind of issue that we're coming to also with the changes in agriculture that we might face in the next century just from global warming. You have to be able to make up those food losses by shipping food from some other place. Adjusting to that takes a long time.

Even now there are lots of places in the world, especially in Africa, where there are people starving to death largely because of droughts, but exacerbated because there's some conflict going on that prevents food being brought in. There are all these problems in human society related to getting along with each other and transporting food to places where there's something bad happening.

Conn: Then continuing with the idea of things getting really bad, can you guys touch a little on the idea of runaway temperatures in climate change? Is that a possibility?

Toon: My group has looked at runaway on the Earth. Someone who had read this study remarked that they were really happy that we'd given them another half a billion years to exist on the planet, because a few billion years from now, the Earth will probably lose the water on the planet and go into what's called a “moist greenhouse”. At least in our calculations it doesn't really run away and boil the oceans, it's just the water becomes so abundant in the upper atmosphere it escapes to space, and we dry out like Venus, for example, is very dry right now and probably did go through a moist greenhouse phase.

But in the near term, I don't see any possibility that the Earth is going to go into a sudden runaway. On the other hand, once you get up to temperatures that are about 20 degrees warmer than the average in the planet, 20 degrees centigrade warmer, people become unable to function just because they can't dissipate the heat from the environment from their bodies.

It's a function of humidity as well as temperature, but, nevertheless, you can have large fractions of the planet become uninhabitable for humans. We can air condition everything and stay inside. That's not really a runaway, but it is a physiological problem for human beings. Depending on how much CO2 goes up, we're not that far from getting into a situation like that in the next century some time.

Conn: Okay. Of all the research you've both done and read and the public reactions you've seen to various research, what worries you most?

Trenberth: We're way behind in terms of what is needed because if you start really trying to take serious action on this, there's a built-in delay of 20 or 30 years because of the infrastructure that you have in order to change that around. Then there's another 20-year delay because the oceans respond very, very slowly. If you start making major changes now, you end up experiencing the effects of those changes maybe 40 years from now or something like that. You've really got to get ahead of this.

This is what scientists have been telling politicians around the world for some time, and yet the political system has been very slow to respond. Now in the Obama administration, they began to seriously respond to this. They developed within the US the Clean Power Plan, and President Obama played a leadership role in forging the Paris Agreement in 2015, December.

This was the US playing a substantial leadership role in helping to forge a pretty remarkable agreement, because it's very hard to get all of the countries, 190-something countries around the world, to reach a unanimous agreement that we should do certain things. Even so, there were no real penalties associated with this. A lot of it was voluntary in various ways. It requires the US to continue to show leadership.

Now, with the last election, a lot of this is disappearing, it seems. Now this is potentially a substantial set back on an international basis. Without the US leadership, and the US being a major contributor to the climate change problem, why should other countries respond? Potentially, we can all point fingers at each other, but we can go down this rat hole of self-destruction rather than working together and recognizing that we're all inhabitants of spaceship Earth together. We have to begin to treat it much more that way.

The atmosphere is a global commons. It belongs to everyone. The air that's over the US a week later is over in Europe, and a week later it's over China, and then a week later it's back over the US again. If we dump stuff into the atmosphere, it gets shared among all of the nations and, similarly, with other countries.

We have to address this as a global problem, but we really don't have any global government. The United Nations is quite weak in this regard. And US leadership, I think, is essential, and that is now lacking.

Toon: I think we've mentioned quite a few issues already in this conversation. The first problem is that there's a long time lag to convert our energy systems into something that is not dependent on fossil fuels. There's a long time lag.

Somewhere out there, there's a tipping point. We don't know where it is exactly. If it's two degrees centigrade, that's not that far from now. It's probably another 40 years or something like that to reach that tipping point, but there's other possible tipping points.

That was based on losing control of the ice sheets, but there's also the ocean acidification problem. We don't know where that kicks in biologically because it involves all these complicated ecosystems. There's a problem with people not being able to control their heat balance outside and within their bodies, and go outside and other animals will have that problem.

There's a problem that organisms are used to evolving and compensating for things, but not on a 40-year timescale. They're used to slowly evolving and slowly responding to the environment, and here they're being forced to respond very quickly. That's an extinction problem. If you make a sudden change in the environment, you can cause extinctions.

We don't have any idea, or any very specific idea, about when some of these things will occur, but we know that if we keep doing what we're doing, some of them are going to occur some time in the future. To me, the main problem we have here is that we can't wait until we can see that disaster is upon us because that's too late. The world has to be able to believe in the scientific establishment enough to say, "Okay. We know this problem is happening."

There's hardly any debate in the science community about this anymore. It's not a science debate going on about the reality of this. The problem is technological and political. What do we do about it? There are people developing technologies that will do things that are helpful, and they're even going to make money out of it.

I'm somewhat hopeful that, despite politicians at the global or national scale, people, politically, at the city scale ... If you live in Miami, you know it's going to get bad there and flood, even though the State of Florida denies climate change. There's a conflict going on between a city there and the state which wants to deny things and the city which can tell it's getting flooded already.

I'm hopeful, at the local level, things will happen, I'm hopeful that money will be made out of converting to this other energy system, and that those things will move us forward despite the inability, apparently, of politicians to deal with things. We can see our own government is just paralyzed. It seems to be unable to deal with anything, not just climate change. Even in the face of obvious problems that they can see happening, they’re not dealing with them. That's very concerning. We just can't wait through this inaction, we have to take action at the lower levels if the higher levels won't act.

Conn: Along similar lines, I was really horrified… Last year, I did my own carbon footprint. For the most part, it was great until I added in just a couple of flights that I'd taken. I assume we have to deal with this on a governmental level, but is there more that those of us who believe in climate change should be doing? Is it helpful if those of us who believe actually start taking more action, or does this all have to be happening on a larger scale?

Trenberth: There's certainly a lot of things you can do as an individual, but they really don't solve the problem. I like to point out that even if you don't have solar panels on the roof of your house you can use solar power by drying your clothes rather than putting them into a clothes dryer. Actually, that's quite a good thing to do because putting them in the clothes dryer actually generates a lot of waste energy. Riding a bicycle, using a smaller car, mass transportation – I take the bus to the airport when I do go to the airport, but I do have to fly now and again. Those kind of things are a bit worrying.

The approach that was taken by the Obama administration was a regulatory approach because the Congress would not go along. It was done under the Clean Air Act under the Endangerment Finding that occurred. As a result, it was putting in place certain carrots and sticks that were designed to help increase sustainability and encourage transitions away from fossil fuel-based energy and electricity in particular to more renewable forms of energy.

The real way of doing this is probably to create other kinds of incentives such as through a carbon tax, as often referred to, or a fee on carbon of some sort, which recognizes the downstream effects of burning coal both in terms of air pollution and in terms of climate change. That's currently not built in to the cost of burning coal, and it really ought to be.

If that kind of thing could be implemented, and it's been talked about also even by Republicans on the national level, then suddenly the whole economics and the balance of the way in which you go about doing things changes. It would really empower the private sector to make major changes. I do think some wonderful things could actually happen if that were to take place.

That would be the thing I would advocate more than anything else is, let's see if we can put a price on carbon. If you do it gradually and build it up over time, then it doesn't have to be disruptive. In fact, it can be a major positive force for change in various ways, and I think some wonderful things could happen.

Conn: And Dr. Toon did you want to add anything?

Toon: I think that during the Obama administration, they basically realized that the science was clear, and it's not an issue of needing more research to be sure that this is a problem. There is need for more research, particularly viewing the Earth from space and seeing what's happening and making sure we watch the ice caps and measuring the deep oceans. We do need to monitor the environment. I'm sure there'll be surprises there about things that are happening.

But this is not really a question anymore about whether climate change is occurring or not. It certainly is occurring. It isn't a matter of belief, it's a matter of fact. You can measure all these things and see that the climate is changing. It's not a belief issue.

However, how do you respond to that? What do you do? At least in the United States, it's very clear that we're a capitalistic society, and so we need to make it economically advantageous to develop these new energy technologies.

For example, we solved the ozone hole problem. Back in the 1980s, companies like DuPont opposed any regulations being put on chlorofluorocarbons until they discovered that their patents were expiring, and they could make money by having new compounds produced. All of a sudden they got on board, and that caused an economic incentive for them. The offending chlorine compounds were banned, and the ozone hole is apparently starting to recover.

There's not quite the same answer to this problem of carbon dioxide warming, but, nevertheless, there is the similar thing of the renewable energy sources can be less expensive and less damaging to the environment, less offensive to look at than some big power plant somewhere belching smoke out on the atmosphere. The United States could do something like the carbon tax that Kevin just mentioned.

My suspicion is we won't do that because of the opposition from various groups that have somehow made this into a religious conflict. However, I think anybody who's been to China can see that they have a very strong problem in China, which is burning coal. The air pollution is very bad there. Large numbers of people are dying from it. They're going to be highly incentivized to start using more renewables. They are leading the way at the moment in producing renewable energy.

I suspect they'll capture that market, and eventually, the United States will wake up and realize they've lost another market, just like they did in automobiles to Asia. For similar reasons, the United States was resistant to coming up with more fuel efficient, better designed, more reliable cars, refused to modify the car industry for a long time. The Asians did that and took it over. The same path is being followed here with renewable energy.

I suspect that we're going to see the rise of China and Asia in developing renewable energy and selling that throughout the world for the reason that it's cheaper and they'll make money out of it. We'll wake up behind the curve, just like we did with automobiles.

Conn: Okay. Any final thoughts?

Trenberth: This relates to whether the policies that are being made are grounded in evidence in science. At the moment, in Washington, they do not seem to be. There are these alternative facts and so on, and there's no science advisor.

Coming up, as we record this, is the March for Science on the 22nd of April. Then the following week, there is March for Climate on April 29th that is trying to send a signal to Washington at least that people are very concerned about the way things are going and that we need to do things that are evidence-based and sound. So pay attention to these things, and I hope you'll join me and others in marching.

Toon: This kind of problem was not historically political. For example, the Environmental Protection Agency was founded by Richard Nixon, the Clean Air and Water Act was founded by the elder George Bush, the Montreal Protocol was established by the elder George Bush. If you're a conservative, you're trying to maintain the Earth the way that it was and the way that it is. It's part of conservative philosophy to take actions to maintain the environment.

How we've drifted into this situation where science has become a political football is not clear to me, but it isn't historically the way it was. We do have to realize that there are facts about the Earth and that there are things that are happening that people understand. We have to take actions based on science, based on understanding, and not just based on the way we wish things were.

Conn: Great. Thank you both so much for joining us today.

Toon: You're most welcome.

Trenberth: You're welcome.