Hi Reddit! We’re Katharine Hayhoe from Texas Tech and Bob Kopp from Rutgers, we want to learn everything we can — about this inadvertent and unprecedented experiment we’re conducting with our only planet, and what it means for our human systems and the natural environment. Ask us Anything!

Abstract

We’re climate scientists Katharine Hayhoe from Texas Tech and Bob Kopp from Rutgers. We were both Lead Authors on the recent Climate Science Special Report (https://science2017.globalchange.gov/) that summarized the very latest science on what is happening to our planet. We’re here to talk about how our climate is changing, what causes it, what to expect in the years ahead, and what risks this poses to us, our families, the economy and the places where we live.

We'll be back at 12pm ET to answer your questions, so please — ask us anything!

The AGU AMA series is conducted by the Sharing Science (sharingscience.org) program. Sharing Science: By scientists, for everyone. More at sharingscience.agu.org.

Dr. Hayhoe, you speak a lot about how you are able to successfully communicate the seriousness of climate change to evangelical Christians, a notoriously conservative demographic, by framing it in terms of shared values.

As a young agnostic climate scientist who has only lived in liberal strongholds like San Francisco, Seattle, and Boston, how can I connect with red-state conservatives, who represent the majority of the remaining doubters of anthropogenic climate change? Should I even try?

aClimateScientist

Thanks for asking!

First of all, talking about climate change is one of the most important things each of us can do as individuals. Surveys have found that about 75% of people in the US don’t even hear someone else talk about it (let alone talk about it themselves) more than once or twice a year. 25% of people say, never.

But how do we talk about it with people who might not agree? I’ve found that the most effective way to start is not with the science. And of course that’s tough for those of us who are immersed in the science 24-7 -- but the most effective way to start is by doing something that often feels a bit uncomfortable for us scientists and that’s bonding over genuinely shared values, concerns, loves, and even fears. What do you have in common with the person/people you’re trying to talk with? Do you enjoy hiking? The outdoors? Want to talk about saving money? The future of your kids? Rotary club members? Live in the same city? You get the picture. Obviously faith is not going to be one for you, but the good news is that there are so many other things we can connect on.

Then next, connect the dots between that shared value and a changing climate, starting from the heart, not the head. “I’m concerned about the safety of people serving in our armed forces, like my cousin X. Did you know that the Pentagon says climate change is a threat multiplier…?” or “My daughter has problems breathing when the air pollution gets bad. We had a scarey time last year when we had to take her to the hospital. Did you know that over 200,000 people in the US die every year from air pollution from burning coal and oil?” or “The political partisanship is so frustrating, it feels like they will never get anything done. That’s why I’m so excited about the bipartisan Climate Solutions Caucus in Congress. You’re only allowed to join if you do so with someone from the other party and so far they have 62 members!” and of course “I believe that we are to love others as God loved us. I am very worried about the people living in X because they are being devastated by unprecedented floods as a result of a changing climate.”

If we need to do any explaining -- yes, climate is changing and here is what we see happening right here where we live; yes, natural cycles are real but right now according to natural factors we should be cooling, not warming; and yes, climate change affects the polar bears but it affects us right here too. In California, we get 50% of our water from snowpack and it is melting faster and more falling as rain rather than snow every year. -- then here is the point where we can do that.

But the biggest and most important thing to end with (or even just talk about entirely) is SOLUTIONS! Because, 99.9% of the time, the real problem people have with climate change isn’t with the science. The science in our climate models is the same science we use in our stoves, fridges, and airplanes every day. No, the real problem is with the perceived solutions: that the government will use it as an excuse to destroy the economy, control our personal freedoms, and let China (and the Antichrist) rule the world.

What types of solutions? Elon Musk’s solar roofs. How much my power bill dropped when I switched to LEDs. How I love the local farmer’s market. How eating lower down the food chain makes a huge dent in our carbon footprint and it saves $$ too. How China is investing $360B in wind and solar energy, far outpacing the US. How Texas leads the US in wind energy and the biggest Army base in the US, Fort Hood, just went 100% renewable to save taxpayers over $150 million. How India set the record for cheapest solar this year. How the museum of coal mining in Kentucky put solar panels on its roof. How a Chinese company is re-training Wyoming coal miners to do wind energy installation.

Hardly anyone will disagree with that - and you may find new, surprising areas of agreement as well!

I talk about this more in our Global Weirding episode, “if I just explain the facts, they’ll get it, right?” https://www.youtube.com/watch?v=nkMIjbDtdo0

This Global Weirding episode talks specifically about Christian values and connects the dots between them and climate change: https://youtu.be/SpjL_otLq6Y

And here’s a longer lecture I gave at the University of Arizona last year, where I lay out this approach in more detail: https://youtu.be/f50b_svjOkQ?t=353

And finally, a study testing whether this actually works. I was on pins and needles waiting for the results of this one! https://www.theguardian.com/environment/climate-consensus-97-per-cent/2017/aug/28/study-katharine-hayhoe-is-successfully-convincing-doubtful-evangelicals-about-climate-change


More a personal question than a scientific one. Hope you don't mind:

How do you stay motivated while staring the reality of climate change in the face everyday?

recentfish

Katharine here - thank you for asking. This is one of the biggest questions I get. Because for sure, the science doesn’t give us much hope. Nearly every time we look -- as you can see from some of Bob’s answers to other questions -- things are happening faster, or to a greater extent than previously thought.

Here’s the thing. Hope is not a passive emotion. If we want it, we have to roll up our sleeves and go out and look for it.

Where can we look for it? In people, in what’s being done here in North America and around the world.

We often picture climate change as a giant boulder standing dead still that needs to be rolled up a hill and no one else cares. But in reality, today that giant boulder is already starting to gradually roll downhill and there are many millions of hands on it, pushing. Maybe we just need a few more!

So, what gives me hope?

The “We’re Still In” movement. So many US cities, states, businesses and investors have committed to staying in the Paris Agreement that, together, they are the 3rd largest economy in the world!

The bipartisan Climate Solutions Caucus - half Democrats, yes, and half Republicans! Real, elected ones in Congress, all committed to fixing this problem.

The amazing tech innovations we hear about every day: Tesla’s new electric truck. Algae fuel for airplanes. Electric airplanes. Solar fabric. Floating solar farms on flooded open pit coal mines. The powerwall.

The unlikely allies. Young Evangelicals for Climate Action. The US National Association for Evangelicals. (yes really). RepublicEn, planning free market solutions to climate change. The Niskanen Center, discussing Libertarian solutions. Relief and development orgs like Oxfam, World Vision, Plant With Purpose, Tearfund.

But this information doesn’t come knocking on the door of our brains. We have to join organizations that help us act. We have to look for stories and news on others who are acting. So that’s why I try to look for it myself and post so much of it on my Facebook page and my Twitter feed.

Because without hope, we’ll become a self-fulfilling prophecy. Only with hope do we have a chance, a hope, to fix this thing.


Do we have any predictions about larger trends than the warming we're seeing now? E.g., do we expect temperatures to keep rising past the maximums we've estimated in other interglacial periods or to otherwise disrupt the glacial cycle?

downwithsocks

Bob here. Thanks for participating in this AMA - it's a pleasure to be here!

Global average temperature is already about as high as some estimates for the Last Interglacial period, about 125 thousand years ago. The Last Interglacial was warmer than our interglacial was (even though there wasn’t any fossil fuel combustion of course!) because the Earth’s orbit was shaped differently, and global average sea level was about 6-9 meters (20-30 feet) higher than today. David Archer did some work about a decade ago which showed that an amount of CO2 emissions roughly consistent with the Paris Agreement is enough to decisively prevent glaciation for the next 130 thousand years. (http://dx.doi.org/10.1029/2004GC000891) and this paper concluded that the next glacial maximum should naturally have occurred sometime in the next 1500 years but we have “indefinitely delayed” it. https://www.nature.com/articles/ngeo1358


Hi! Thank you for doing the AMA!

  1. What was the most difficult change to measure?

  2. Regarding the urban heat island effect in 10.4: Urban Environments and Climate Change, is there a tech or process, excluding albedo mods, that can be used to capture the increased temperature and treat it as an input to a useful process?

  3. Have you noticed changes in human behavior related to increasing temperatures?

Thank you for the research. It is well formatted and easy for me to navigate and understand. :)

BlueSky1877

Katharine here.

On the first question: changes occurring in remote locations where people don't live, and that are typically very extreme climates, are tough to monitor. The middle of Antarctica or Greenland, the intermediate or deep ocean, even the remote Amazon ecosystem. Yet those are some of the most sensitive aspects of our climate system and therefore the most important to understand!

On number two, green roofs are a big thing - as is renting out rooftops for solar. Chicago and NYC are leaders in these areas.

And on the third question, yes, we humans absolutely respond to our environment. And unfortunately, the impact of heat on our bodies makes us annoyed, causes us to sleep less, and even triggers violence!! There is a large and growing body of literature that tracks our physiological response to warmer temperatures. Here is a recent review: https://www.psychologicalscience.org/observer/global-warming-and-violent-behavior


Hi guys, very nice of you to be here for our questions!

1: So, can we really stop climate change in span of one human life? Because climate system is so complex and slowly reacting, it's now IIRC still trying to balance all those emissions we have put in it hundred years ago and if we all dissapeared tomorrow, climate would still be changing and warming for some decades.

2: Did you studied and predicted some effects to the other countries than the US? For example some huge slope deformations (e.g. landslides) in Himalyas?

3: Is desertification now another negative positive feedback like glaciers melting?

BlackViperMWG

Bob here.

(1) One striking finding out of the recent literature is that the total amount of warming we experience is roughly proportional to the total amount of carbon dioxide we emit, that this warming is largely realized within about a decade of emission, and that it lasts for well over a millennium. So bringing emissions to zero should stabilize warming relatively quickly. Unfortunately, there are also positive feedbacks triggered by the warming that cause more greenhouse gases to be emitted -- for example, permafrost melt in the Arctic. So the approximation breaks down in that regard. But the speed with which we experience benefits from cutting emissions is often misunderstood. Ricke and Caldeira (2014) have a nice discussion: http://iopscience.iop.org/article/10.1088/1748-9326/9/12/124002/meta?gridset=show

(2) The National Climate Assessment by law is focused on climate changes in and impacts to the United States. Our volume, the Climate Science Special Report, has a chapter discussing global changes but primarily focuses on physical effects in the US. The draft of the second volume, which focuses on impacts, does have a chapter discussing climate impacts on US international interests.

(3) Desertification could be a positive feedback if it leads to a reduction in biomass on land.


Where do you want your children, grand-children, and great-grand-children to live, knowing what's coming? I think about it often. Where can my descendants live most safely and happily?

Bubbock

Bob here. I want my descendants to live on a planet where humanity has attained the maturity to manage our planetary-scale power wisely and is either bringing (for my children) or has brought (for later generations) net greenhouse gas emissions to zero, or is even accelerating the removal of greenhouse gases from the atmosphere. Even so, it’s likely that a good deal of coastal land will be swamped -- we estimate a land currently home to about 100 million people could be underwater by 2100 even under a low-emissions pathway -- so I’d be careful investing in coastal property for them.

If we remain an immature planetary civilization, than the Climate Impact Lab’s study of the economic impacts of climate change in the US suggest that, within the US, the Pacific Northwest might experience the least harm from climate change. (Of course, it does have a pretty substantial earthquake risk). See http://www.impactlab.org/research/estimating-economic-damage-from-climate-change-in-the-united-states/


Where do you want your children, grand-children, and great-grand-children to live, knowing what's coming? I think about it often. Where can my descendants live most safely and happily?

Bubbock

When I [Katharine] am thinking long-term, I look for thriving urban centers that take sustainability and resilience seriously, surrounded by ample farmland that provide local food and good water resources that will not be significantly affected by a warming world. And with all or at least most of their infrastructure well above sea level. I am keeping my Canadian citizenship for a reason!


Dear Dr. Hayhoe,

CCL fan here! Thank you so much for joining us. You are seriously my hero for the work you have done.

Can you give some examples of how you've successfully persuaded a climate skeptic, and how we can emulate this ourselves? I assume there are no shortcuts and it just take a lot of time and trust.

(Is all this in the book? It's on my reading list but I haven't found a library that carries it yet.)

Kamala_Metamorph

Thanks Kamala!

The first place to start is with an understanding of who we’re talking with. Are they cautious? Disengaged? Doubtful? Or Dismissive?

If dismissive, then there is really no point to engaging because their rejection of the science has become so internalized that it is like asking them to cut off an arm or remove part of their brain to change their minds about climate change. An angel from heaven with brand-new tablets of stone reading “global warming is real!” in letters of flame wouldn’t be enough, so why would I think I am? I’m not.

But as you can see from the figure linked here, even though dismissive people are by far the loudest, they are only a tiny fraction of the overall population (even though they appear to be disproportionately concentrated in DC at this moment!). Many more of us are doubtful, disengaged, or even cautious.

Figure: https://www.researchgate.net/profile/Connie_Roser-Renouf/publication/50597255/figure/fig8/AS:341634710556703@1458463470988/Figure-1-Proportion-of-the-US-adult-population-in-the-Six-Americas.png

So for those people, the important thing is to start where they are at, with the things they care about. And by doing so, we can build a positive conversation that goes somewhere good -> ending with solutions! -> rather than ending with our heads exploding.

I go into this in more detail in my answer to the question above, about talking to evangelicals. But to your point, has this changed minds? The answer is YES. We even have peer-reviewed proof! https://www.theguardian.com/environment/climate-consensus-97-per-cent/2017/aug/28/study-katharine-hayhoe-is-successfully-convincing-doubtful-evangelicals-about-climate-change

And when I talk with people who share with me that they’ve changed their minds -- many of whom lurk on my Facebook page for months or even years before engaging! -- what they all say is, I felt like we shared [XXX] or had [YYY] in common so I listened to what you said and it made sense.

Starting with that common ground is key to opening both of our ears to each other.

Check out Karin Kirk’s fascinating “Common Ground” climate conversations that attempts to do just that! https://www.yaleclimateconnections.org/2017/10/seeking-common-ground-in-climate-change-dialogs/

And yes: we almost have the second edition of our book out. But it doesn't talk about this! This video is a lot more detailed -> https://youtu.be/nkMIjbDtdo0


How likely do feel climate change is going to lead to catastrophic wars? My intuition says this is unavoidable now.

01-MACHINE_GOD-10

Bob here. There’s a growing literature on the relationship between climate and conflict, both interpersonal conflict (e.g., violent crime) and intergroup conflict (e.g., civil war). More extreme temperature and rainfall does have a tendency to increase the likelihood of violent conflict. But it’s a risk amplifier: I think it’ll stay very hard to say that climate change ‘caused’ a conflict, though it may make conflict more likely.

On the other hand, climate change is happening in a world that’s experienced a long-term, multi-century decline in violent conflict, so the net effect may be more to slow this decline than actually make the world more violent than it has been over the last few decades.

Maintaining the overall health of the international order is probably the most effective way of avoiding catastrophic war.


Hi, my comment got stuck as a reply to the AMA notice (sorry). I hope it is not too late to make it:

Hi, Good luck with what you're doing. I wonder why most public concern about global warming has to do with things like sea level changes and the economy -- is it true that the long term consequences (over the next 1000 years) would have more to do with extinctions?

Why do people pretend that they care about things like holiday resort receipts instead?

Also, are there other long term dangers to the environment besides global warming? I'm thinking, for instance, chemical, nuclear, and now genetic pollution (though small organizations being able to modify seeds and pollen) are going to take place. Especially in the case of nuclear and genetic pollution, these have the possiblity of being essentially permanent. I don't know of any regulalatory process that could stop his from further escalating. Are your analyses restricted to thinking about CO_2 and climate?

A guy recently at Bristol University tried to make an indicator of what should be acceptable, and he seems to have based it on immediate quality of life (he called his indicator 'j'). Is it just politics that makes people think this way?

anon5005

Bob here.

Most people don’t think too much about what the world will be likely centuries from now. Yet we have active political debates about a Constitution written two centuries ago and follow religions that are millennia old. So I think many of us do, at some level, care about the legacy we leave to the world centuries and millennia from now.

The irreversibility of some of the changes we’re making to the global environment are a big issue, and many millennia from now will leave an indelible signature in the geological record. These changes include sea-level rise that has the potential to continue for millennia, and temperatures, which will remain elevated for over a millennia. Such changes will characterize a new world to which humans and ecosystems will have to adapt. Humans probably will make it; many species, already stressed by forces such as global re-mixing and habitat disruption, may not. I would argue that all of these should be of concern.

In terms of other environmental risks, the ‘planetary boundaries’ framework provides one nice way of looking at these. See http://www.stockholmresilience.org/research/planetary-boundaries/planetary-boundaries/about-the-research/the-nine-planetary-boundaries.html.


Hi, my comment got stuck as a reply to the AMA notice (sorry). I hope it is not too late to make it:

Hi, Good luck with what you're doing. I wonder why most public concern about global warming has to do with things like sea level changes and the economy -- is it true that the long term consequences (over the next 1000 years) would have more to do with extinctions?

Why do people pretend that they care about things like holiday resort receipts instead?

Also, are there other long term dangers to the environment besides global warming? I'm thinking, for instance, chemical, nuclear, and now genetic pollution (though small organizations being able to modify seeds and pollen) are going to take place. Especially in the case of nuclear and genetic pollution, these have the possiblity of being essentially permanent. I don't know of any regulalatory process that could stop his from further escalating. Are your analyses restricted to thinking about CO_2 and climate?

A guy recently at Bristol University tried to make an indicator of what should be acceptable, and he seems to have based it on immediate quality of life (he called his indicator 'j'). Is it just politics that makes people think this way?

anon5005

So often we feel as if climate change should be higher on our priority list. But the reality is, I [Katharine] don’t think climate change should even be on our priority lists at all. We care about a changing climate because it affects all the other things we already care about: yes, even our vacations (often in high-risk locations at sea level or that need snow) and our coffee. We don’t need to instill new values into most people; we just need to connect the dots between what we already care about and climate change.

But at the same time, our human psychology is working against us, right? We are terrible at long-term decisions. We avoid big problems. And when we feel like we can’t fix it anyways, why would we care? Disengaging is the only effective defense.

That’s why hope is so important. And as I said above (see previous question), hope is essential to fixing this problem. Without hope, we will be a self-fulfilling prophecy. We need to feel as if we can fix this in order to have a real chance of actually doing so.


How likely do you think the highest emissions scenario (RCP 8.5) is? Also, how do you think the decline of oil supply will impact energy trends? more unconventional fossil fuels or more renewables?

bluejule

Good question! In chapter 4, we conclude that, "the observed increase in global carbon emissions over the past 15–20 years has been consistent with higher scenarios (i.e. RCP8.5). In 2014 and 2015, emission growth rates slowed as economic growth has become less carbon-intensive" -- but we know now that it ticked back up in 2016.

As someone who works with the RCP scenarios every day, I [Katharine] would say that the probability is fluid: and in fact, by studying the impacts of RCP8.5, we are decreasing its likelihood.

If we didn't know how bad it would be, why change? If we didn't know smoking caused lung cancer, I'd smoke! But knowing what it does, having it presented in gruesome detail, that's what convinced me not to smoke. And my hope (with the research I do, which is quantifying the impacts associated with different future scenarios and different levels of global mean temperature change) is that I'm helping to paint that picture.

Finally, though, if I had to pick a "most likely" future scenario, it wouldn't be any of the RCP scenarios.

It would be one that starts to bend off higher emissions (as in fact we are doing now), but not yet at a rate to meet the 2oC and certainly not the 1.5oC target -- until a decade or two from now, when the sheer magnitude of compound extreme events (which we talk about in Chapter 15) builds up to a collective global "oh shit" moment and our emissions take a rapid dive as people invest in and build out negative-emissions technology as well as shutting down the remaining fossil fuel power plants and getting rid of remaining gas-powered cars. That is my personal best guess.

But honestly - we won't know for sure until it happens, because the thing we are most sure of is that humans are the least predictable and the most uncertain part of any future equation.


Hello - Do you have any suggestions re good sources to keep up with climate news (websites/twitter/etc)? It always seems so depressing.

CaptainMarkoRamius

Yes - you probably saw my [Katharine's] longer answer above regarding what gives me hope!

To that end, I post a lot of positive stories on my FB feed. I follow Skeptical Science's FB feed as well since they tend to curate both the latest science as well as "good news" stories. And I follow a lot of science/tech/environment reporters or news feeds on twitter that will give me this too.


Hi, Thanks for doing the AMA! I have 2 questions: 1). What is something that everyone can do that will make a big difference? (eating less meat, driving less, etc?)

2). What's the most unexpected thing you found in your study?

plups

This is Katharine on question one. One of the most important things each of us can do is, TALK ABOUT IT!

Did you know that about 75% of people in the US don’t even hear someone else talk about it (let alone talk about it themselves) more than once or twice a year, and 25% of people say, never?

And when we ask people, do you think climate change matters to you personally, nearly everyone in the entire country, no matter whether they agree with the science or not, say, NO?

(Very cool public opinion maps available here, by county/congressional district/riding (in Canada): http://climatecommunication.yale.edu/visualizations-data/ycom-us-2016/

And why SHOULD people care about it if we never talk about it, right?

So what can we talk about? Personal actions are a great thing to discuss, particularly if they save us money or are good for us or are cool and fun. And because they are real, immediate, tangible, and hopeful. And because if enough of us act together, we absolutely can make a real difference.

If we want personal actions to do and to talk about, then the first step is to step on a carbon calculator like this one (below) and weigh our footprint. What parts of our life produce the most emissions?

http://coolclimate.berkeley.edu/calculator

For many of us, it might be our diet. Eating lower down the food chain is really important: to cut carbon emissions, to cut our food budget, to be more healthy, and to avoid subsidizing industries that are not concerned about animal welfare. And let’s not forget about food waste! We throw out so much of what we buy, about a third nation-wide - we need to be a lot smarter.

For others, it might be our travel. Mine is flying. So I carefully stack and organize my trips so I can give multiple talks in one place at the same time, then I offset the rest with Climate Stewards (who I know personally and can verify are incredibly careful about their carbon accounting and are doing amazing work investing in local economies in Ghana, Mexico, Kenya and more). https://www.climatestewards.org/

Maybe we love our new plug-in car and can’t stop talking about it. Maybe, like our colleague Peter Kalmus, we’ve become urban gardeners (you don’t want to know where the manure comes from). He wrote an awesome book here about his personal journey with his family, check it out: https://www.amazon.com/Being-Change-Spark-Climate-Revolution/dp/0865718539/

You get the picture! It’s so important to understand and feel like we’re not the only one who cares. And we can only do that by talking about it and by looking for others who are, too.


Hi, Thanks for doing the AMA! I have 2 questions: 1). What is something that everyone can do that will make a big difference? (eating less meat, driving less, etc?)

2). What's the most unexpected thing you found in your study?

plups

Bob here on question two. In terms of the unexpected, this report is an assessment of the literature, not new research. So all the unexpected things were already out in the literature to be assessed. But one striking finding is that climate models tend to underestimate temperature as geologically reconstructed during past warm periods. To us, this suggests that there may be amplifying (positive) feedbacks not well captured in current climate models that may play an important role at higher CO2 levels.


Are there any plans to present the NCA findings to the President?

pnewell

Briefings happen on request and we have not received one.

But here’s the thing. Will this report change his mind? I (Katharine) say, no. And this NYT article says the same. https://www.nytimes.com/2017/11/04/climate/trump-climate-change-report.html

Social science has shown us that arguing facts with someone who has already decided to reject them because they are inconsistent with their ideology and their personal identity just deepens the trench between us. There’s a “backfire effect” where people can even become more hardened in their rejection!

If you watch episode 4 of the first season of the Years of Living Dangerously, you will see this in action. My friend Anna Jane Joyner tries to convince her dad, a super-conservative pastor and leader of a big charismatic ministry, that climate change is real. By the end of the episode, he’s even more strongly in denial than he was before, because he interpreted this as a personal attack on him and his identity. And what do any of us do, when attacked? We defend ourselves, of course. Here's the link to that episode: https://www.youtube.com/watch?v=GSUQZj0xOUs

So if I had 30 seconds with the President, I wouldn’t haul out a copy of this report and start reading through our key messages. I’d keep it short and simple: "Mr President, how do you want to be remembered? As Nero, who fiddled while Rome burned? Or as the hero who saved the world?"

More, on how facts don’t always change people’s minds: https://youtu.be/nkMIjbDtdo0


There are certain consequences of climate change that we are very sure are going to happen, for example that continuing to emit greenhouse gases into the atmosphere will lead to warming of the globally averaged surface temperature.

As you point out in the Climate Science Special Report, there is the significant possibility for unanticipated changes, which some refer to as unknown unknowns, because we don't know if they exist or how impactful they may be.

One might think for example of Marine Ice Cliff Instability, a recently discovered mechanism that accelerates glacier flow and could potentially double rates of global sea level rise (DeConto and Pollard 2016), but is not yet included in IPCC-class climate models.

Two questions:

1) Why should we have any faith in our climate models if we are missing leading order physical processes (in the example above, the added process makes things worse but one could imagine a process that makes things better)?

2) How do you propose the climate science deals these unknown unknowns?

aClimateScientist

Bob here.

Faith doesn’t have a role in science. We need to be critical of our approaches and our tools. For climate models, a key form of critical evaluation is comparing simulations and observations. At a global average level, over the historical period, climate models do quite well. In particular regions, performance varies between models, and so if you’re studying a particular process in a particular region, it’s important to identify those models that compare well. (In this National Climate Assessment, for the first time, the climate projections use a form of weighting intended to handle both model performance and model independence.)

That said, we’ve got a big out-of-sample problem with climate change: we are forcing the planetary climate in ways that the Earth hasn’t experienced in the observational record. In my opinion, paleoclimate data/model comparisons provide a key test, though the challenge with paleoclimate is the potential for significant uncertainty in the data as well as the model, as well as the low temporal resolution. It appears that climate models systematically underestimate temperature change during warm paleoclimates, suggesting that climate models are more likely to underestimate than to overestimate the amount of long-term future change. This is definitely an area that needs more work - and one, I think, that is a key pathway toward identifying unknown unknowns.


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