Science AMA Series: I'm Tom Crowther, a Scientist from Yale University and the Netherlands Institute of Ecology. My research shows how human activity affects ecosystems worldwide, leading to global climate change. AMA!


Along with providing many of the services that support human life and wellbeing, terrestrial ecosystems help us in the fight against climate change by absorbing CO2 from the atmosphere. But our unsustainable use of the Earth's resources is beginning to threaten the health of those ecosystems, limiting their capacity to store carbon. I study how the world's trees and soils are changing under the influence of human activity, and the consequences of these changes for on-going climate change.

In 2016, we published a paper revealing that atmospheric warming will drive the loss of approximately 55 gigatonnes of carbon from the soil into the atmosphere by 2050, with the potential to accelerate climate change by 17% on top of current expectations. We also showed that there are over 3 trillion trees on Earth which are able to absorb much of this carbon, but their capacity to do so is being hindered by the loss of ~10 billion trees each year caused by deforestation, fire and disease/pests. Understanding and preserving these terrestrial ecosystems at a global scale is absolutely critical in the fight against poverty and climate change.

I will back to answer any questions at 1PM EST. Ask me Anything!

Edit: Thanks so much for all of the comments and questions! I'm heading off now, but I'll check in a bit later to go through some more.

Cheers, Tom

Hi Tom, and thank you for doing this AMA.

Growing up, I remember that a big environmental concern was human activity causing ozone depletion in our atmosphere, leading to the so-called 'ozone hole'. It was quite the concern, if I remember correctly. Luckily, strong environmental policy and research advocacy led to the enactment of legislation restricting the use of the chemicals that were causing ozone depletion. And, recent news studies suggest that this approach worked - the ozone layer appears to be 'healing'.

SO my question is, to what extent is this possible for climate change? If humans got serious about reducing CO2 emissions, would we see a similar 'healing' of the climate?


Climate change is a slightly more complicated issue than the ozone hole, so its hard to say for sure. But I am personally confident that we could certainly go a hell of a long way towards stopping it. Of course, it would have been better if we all know about this when it was first uncovered many decades ago, but I am confident that international policies that are intended to reduce carbon emissions, increase carbon sequestration in natural forests and soils have the potential to dampen, and maybe even reverse many of the effects that we have already seen. And maybe there are huge technological advances or improvements in plasma technologies that will also help us to address the growing societal needs without having to release so much carbon into the atmosphere. In short, I think we could be optimistic, as long as the overwhelming message from the science community is considered by decision makers.

Have you ever discussed your science with elected officials or others in government/political positions? If so, how did it go?


Yes. Well without naming names, you can imagine that the response is very partizan. We all have confirmation bias so any new information just fits into our pre-existing agendas and politicians are no different. But if you consider this confirmation bias when discussing these things with climate skeptics, it is often easier to find the middle ground. Most scientists are not saying that we should do anything that limits jobs or economic development. So there really is no reason to avoid the facts on this one.

Any idea why scientists don't really run for political positions, so they could implement policy to fight climate change? As well as many other things that a scientists ability to thinks critically would aid in. I feel like it should be a thing.


Haha. Good question. I suppose people always say that, when you enter politics you have to start dealing with thousands of other issues and its more difficult to keep fighting 100% in the thing you believe in most. I do think it would be good to see more scientists doing that though.

Hi Tom! My university environmental science professor believes that we can't prove climate change is human-caused, due to the fact that the earth's temperature has always fluctuated for thousands of years-- way before humans even existed. How would you argue against this stance? Is it possible to isolate correlations between ozone makeup/human activity as the sole factor affecting the earth's temperature?


Ignoring climate change because we will be plunged into an ice age in 20,000 years is like ignoring a bus because we are all going to die when we are 90 anyway.

The Earth is always going through massive glaciation cycles that take place over tens of thousands of years. We came out of the last glacial period 12 thousand years ago. We would normally be expecting to re-enter an ice age in tens of thousands of years. These fluctuations would also impact humans, but we don't even know what human society will look like in tens of thousands of years.

The problem is that we are undoubtedly causing a MASSIVE fluctuation that is taking place within 100 years. Firstly this means that loads of organisms have no time to adapt and survive, which is leading to massive-scale extinctions. But from a human perspective, it is altering the world in a way that it will no longer be able to support our current (and growing population) for the next couple of generations. We know that our actions can help those people, so we should all try to help.

Welcome to r/science.

I'm currently studying permafrost cliffs in the Arctic - an area undergoing rapid changes at the moment. A lack of quantitative data and suitable models casts a lot of uncertainty on extrapolations of erosion rates and carbon loss in this area. So a certain amount of overlap!

In your own work, what areas do you think are lacking most when it comes to observational data, and what areas are proving the most difficult to model or project changes for?


Well generally, I would say that we dont have enough empirical data on the responses of soil carbon stocks to climate change factors in any parts of the world, and in particular the tropics. I think that more empirical data at a global scale is maybe the biggest limitation that we currently have for projecting climate change. Although Im sure an Earth System Modeler might say otherwise

Thank you for taking your time to do this AMA.

Question: let's assume the worst: The world today doesn't listen, continues to increase production of materials and energy that accelerate the warming process.

Where will we be in 10 years? 25? 50?


That is the million dollar question that we are all trying to figure out. And it is such an important question because it is so difficult to combat climate change if we dont know exactly what it will look like. But there will be millions of impacts that pervade society, ecology and climate. But it is safe to say that the world will be, on average, a couple of degrees warmer by 2050. And the resulting changes in climate will limit the capacity of natural ecosystems to provide the resources that are necessary for society to continue developing the way that it currently is. This resource scarcity will negatively impact local economies and people all around the world in a wide variety of ways. The poorest communities will be the first to be affected, and they will feel the effects most (probably leading to widespread antagonism and migrations the likes of which we are already seeing). But these are just some of the most obvious impacts of climate change, which will probably be coupled with things like sea level rise, extinction of species and extreme weather events

Which areas of the world need to plant more trees in order to maintain their ecosystems? Obviously areas with high amounts of deforestation, but where else would the surrounding areas benefit from new trees?


Almost all areas of the world could benefit from increased tree cover. Deforestation has been widespread and tree planitng can restore habitats. The tropics has the greatest potential for productivity and therefore carbon sequestration.

Why it is so hard for Scientists to talk about human population growth as the first and foremost driver of land conversions, habitat destructions, energy use, and hence all climate related issues? Are we not just talking about side effects if we focus on other things by not zeroing on human population growth? Managing symptoms can only take us so far!


I definitely do not find it difficult to say that. The problem is certainly caused by massive human population growth, and the excessive resource exploitation that comes with it. Certainly tackling that problem with improved education of people around the world is the best way to address so many of the world's problems. But in the climate change debate, we are often talking about how best to improve the world so that it can sustainably support all the people that are currently in it.

Hi Tom! Thanks for doing the AMA. I'm a student at Clemson University studying Biosystems Engineering.

I have read articles that state even if humans were to have some sort of environmental epiphany and suddenly stop contributing harmful greenhouse gases to the atmosphere that climate change is already so well underway it wouldn't change anything as far as sea level rise or other habitat destruction from severe weather goes. My question is, if that is the case, how do we accept climate change and prepare for the future? How do we save these ecosystems when we know there isn't anything we can do to stop the repercussions of the damage that has already been done?


Certainly there are a lot of positive feedbacks that have already begun, so that the climate will continue to change temporarily even if we stopped emissions now. However, this certainly doesnt mean that we shouldn't work to reduce emissions now. Every little that we do will dampen the impacts of climate change weaken the feedbacks. In my paper I showed that the strength of the feedback between warming and soil carbon emissions would be halved if we limited the amount of warming by half. With the appropriate management of our natural resources, we could actually start to increase carbon sequestration in forests and soils, which might negate many of these feedbacks altogether

I currently work for a state park, and I absolutely love it!

We are currently burning the shrubbery in our forests to create the "pre Colonial" forests so our local fauna and fauna benefit from the habitat. How do you feel about prescribed burns? How can I communicate the pros and cons to our visitors and guests?

Thank you for all that you do!


In some areas, replicating natural fire regimes is important for management of healthy forests. This can, for example, help prevent future catastrophic wildfires by minimizing fuels on the forest floor, and it can also help increase overall biodiversity and functioning by promoting those species that rely of frequent fire return intervals. The key is to use it responsibly as one of many management options, and to use it in line with the best available evidence about natural fire regimes in order to improve the overall health and productivity of that specific environment.

I'm just so pessimistic when I see how much we Westerners consume, how much upcoming countries consume and how careless we polute ecosystems that took millions of years to grow. And we humans are still growing exponentially in numbers.. A couple billion more in the next 100 years. Do you have any good news to cheer me up? Am I missing something essential that proves me wrong?


Yes, we have caused devastating damage to natural ecosystems around the world, but this has come with unbelievable technological and societal developments, which have been spectacular. I am writing to you on a laptop from a different country - how incredible is that!? But now that we are able to understand the catastrophic impacts of our activity, we need to fight as hard as we can to become more efficient, and to preserve and restore the stunning ecosystems that we have. A growing body of people around the world are getting into this fight to save natural ecosystems, and the benefit is that almost all activities that we do to restore/conserve nature also have a positive impact on climate change and local economies. There is a huge amount that we can all do to limit climate change - the real challenge is to engage people and make sure that our representatives start to make decisions that allow us to to fight against it without losing all of the benefits that came along with human development

Where do you get your funding?


I am funded by an EU Marie Curie research grant. So they have absolutely no agendas - they just support innovative science. In all honesty, in the proposal that I wrote to get that grant, I proposed that I would do the experiment under the expectation that the massive soil feedback would not exist. But when the results came in, it was very clear that this feedback is a real thing, which needs to be considered in future climate scenarios

I work in the science field. (Aerosol research) Many of the people I work for are actually climate change deniers and they are scientists, they always say that when you want things to grow better in a greenhouse you pump it with CO2 so global warming would be a good thing. They also say that the planet is on a cooling period not a warming period. I'm not sure how to combat these arguments effectively I'm aware of the basic concepts behind climate change but I just don't know enough to disprove them. Any suggestions?


In some scenarios climate change may increase productivity but it is not just a case of 'global warming', evidence suggests that there will be increased climate variability, drought, sea level rise which will reduce productivity, as well as threatening human well being in other ways. Glacial cycles are undeniable but 2016 was the hottest year ever recorded, human caused change is overriding the natural cycles.

I don't know if this is right question to ask here, but assume we continue to harm environment at current level (i.e deforestation, abuse of natural resources and other actions harming environment will not decrease) when will this have serious effect on life of average people in developed world ?


Climate change is already having a massive impact on many people's lives. As you correctly note, people in the developed world are less obviously affected at the moment. But there are many examples of extreme weather events (storms, hurricanes, flooding etc) that have negatively affected people already. There is massive drought in California, which is the direct result of climate change and is affecting many people and their livelihoods. But even more worryingly, there are many studies linking increased levels of antagonism between people to the increasing resource scarcity. This fighting generally leads to mass migrations like what we are seeing in Syria, and is having a direct impact on people in the developed world. In fact, I would argue that these effect have directly contributed to the current political climate of fear and isolationism.

What is currently the most robust piece of quantitative climate-change research and what academic journal is it in? I'm an associate professor in the social sciences, and I'm kind of morbidly curious if I would even understand the math, the logic, and the lingo.


If you only want to read a single paper on the topic, something like the famous “hockey stick graph” which appears in this 1999 paper by Mann, Bradley & Hughes is fairly convincing. Again, as I mentioned above, a scientific fact is just a piece of information where theory is overwhelmingly supported by empirical evidence. This is a really illustrative example of some of the evidence underlying climate change research.

I live in Atlanta, Georgia and over the past 20 years have noticed a large amount of root exposure and lowering soil levels likely related to what you're studying.

How will the exacerbated exposure of roots caused by soil degradation and insufficient snowpack affect forestal ecosystems? Where would we be seeing mass dehydration and treefall? Can soil itself recover?


I'm not an expert in this but the degradation of forest soils is a major contributor to climate change. It takes over 200 years to create a centimetre of soil so recovery of soil will be very slow. Trees roots grow throughout the trees life so although they are generally only 2m below the surface they will penetrate the soil in response to soil erosion.

Hi Tom, Have you, or some of your colleagues,been affected by the freezing of some grants funding research on climate change? How is it possible to overcome a decision like that?


Personally I haven't been affected. Recent political developments mean this is an increasing worry for many researchers. There are a range of non-government funding sources available and I hope these will act to keep alive research areas where government funding has been frozen

Clearly something is happening, the climate is changing and we can tell with our own senses. But how can we be sure if it's also part of a natural cycle or not? Human activity must be responsible for a part of it due to releasing massive amounts of CO2 and whatnot into the environment and massive deforestation over the past 250 years or more. But are you aware of a number of natural cycles which are also contributing to climate change?

Are you familiar with Gregg Braden? What do you think about his research concluding that the climate change is related to a number of natural cycles which he shows graphs of that line up with where we are in the cycle? I'm sure it's somewhere on the internet too but I personally found it in his book Deep Truth as well as his Missing Links series on Gaia tv. He references the ice cores they took from the Antarctic which date back over 400k years showing the cycles of climate change.


I am not familiar with Gregg Braden's work so I can't comment directly, but to reiterate a similar point of mine above:

Ignoring climate change because we will be plunged into an ice age in 20,000 years is like ignoring a bus because we are all going to die when we are 90 anyway. >The Earth is always going through massive glaciation cycles that take place over tens of thousands of years. We came out of the last glacial period 12 thousand years ago. We would normally be expecting to re-enter an ice age in tens of thousands of years. These fluctuations would also impact humans, but we don't even know what human society will look like in tens of thousands of years. >The problem is that we are undoubtedly causing a MASSIVE fluctuation that is taking place within 100 years. Firstly this means that loads of organisms have no time to adapt and survive, which is leading to massive-scale extinctions. But from a human perspective, it is altering the world in a way that it will no longer be able to support our current (and growing population) for the next couple of generations. We know that our actions can help those people, so we should all try to help.

In other words, regardless of the potential for other natural cycles to offset our impacts over the next thousand+ years, we know we are currently causing a huge impact on the Earth's climate. If a bus was speeding at you at 80 mph, would you refuse to get out of the way simply because there is a slight chance it might turn before hitting you, or you might only break one bone if it does? All we can do right now is make our choices based on the best available evidence, and that evidence suggests that humans are having a massive, rapid effect on the climate.

Every 6 months or so there's a new report out something to the effect of "WE HAVE REALLY HIT THE POINT OF NO RETURN NOW." My question is, if it's really too late, if we're totally screwed already, what point is there in taking action to prevent/slow/reverse climate change? (like, is it really too late? have we lost? if so, why fight?)


There's a huge amount we can do to dampen the effects and limit the damage caused by climate change. But we do need policy makers to take coordinated action very soon.

Hi, how do you think Donald Trump's position on climate change will impact upon the continuing research into this phenomenon? Do you think that he will be extremely detrimental to any progress towards a green future?


Not to get too political about this, but definitely governmental involvement and support is critical both for ongoing research and for investing in green infrastructure. Creating an atmosphere conducive to collaborative and creative interdisciplinary research will be needed to address these issues going forward. Those organizations that don't listen to the overwhelming body of evidence in support of climate change will fail to be global leaders in the future energy economy.

When you told us to make soil plates for our fungi project in Cardiff, did you know it would be a ball ache of such catastrophic proportions that it still gives me nightmares?


Haha. Yes, yes I did

I'm sure you've heard of the "Reproducibility Crisis". Rampant P-hacking, low study size, journals not publishing articles that disprove previous articles etc. As a physicist, this has made me very doubtful of what I've read in certain fields such as psychology, medicine, nutrition and sports "science". Do you think your field is affected by this?


This is actually something I have addressed in relation to previous studies. The issue of small sample sizes and potential confounds can definitely be a problem when you’re talking about smaller exploratory field studies. However, when it comes to the datasets underlying global climate models and the change they predict over the course of the next century, they’re supported by an overwhelming amount of mutually confirmatory data that arise from a range of completely independent methodologies. So when you’re working on this scale, I think it becomes much less of an issue.

Hi Tom, I know that meat industry is also affecting climate change. However, giving up meat for people especially in western countries has seemed like a big deal (including Christian belief, that man rules over all life forms). Could you please help me understand how I can educate people around me about this, and make them eat less meat? Maybe if you can throw in some alternatives, that'd be great.


Giving up meat completely is a big ask for a lot of people but if all meat eaters had meat free meals just a few more times each week this could have a huge impact. Don't replace the meat, make a vegetarian dish!

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