Science AMA Series: I’m Corinne Le Quéré, Professor of Climate Change Science and Policy at the University of East Anglia (UEA) and Director of the Tyndall Centre for Climate Change Research. I work on the interactions between climate change, carbon emissions and sinks. AMA!


Hi Reddit!

My name is Corinne Le Quéré. I am a scientist and Director of the Tyndall Centre for Climate Change Research. I work on the interactions between climate change and the carbon cycle. I scrutinize the evolution in carbon emissions from fossil fuel burning and deforestation, and where these carbon emissions end up in the natural environment. This includes the atmosphere, land and ocean carbon sinks. My research is based on data synthesis and models to identify the trends and their drivers. I will be joined by Dr Manoj Joshi, a climate scientist at the UEA’s Climatic Research Unit, who works on climate models and the physical processes underlying climate and climate change.

We look forward to answering lots of interesting questions about the recent trends in carbon emissions and sinks and how these have affected the climate over the past decades.

I will be back at 4 pm GMT (11 am ET) to answer your questions, ask me anything

PS I’ll be giving a lecture on this topic in London in a couple of days, for which UEA have made a short promo video that you can watch here:

Edit1: Thanks everyone for your excellent questions and your interest in our research. I'm afraid we've run out of time now but if you're interested in watching my lecture on Thursday in London or live on Facebook hope to see you there!

Do you think that reforestation would be an effective carbon sink? Looking at some rough numbers it seems plausible:

So, if instead of spending time and energy to cut down forests, we'd been re-planting forests and had added 7% more over the last 13 years it seems like it would've eventually sequestered the equivalent of 50% of human GHG emissions from that period.


hi reddit, first of all, thanks for all the questions everyone! I’ll start here on carbon sinks. Yes reforestation is an effective carbon sink as long as the forests are not cut later on! In fact there is already quite a lot of reforestation going on in abandoned agricultural land. The numbers are not so high though. Carbon emissions from deforestation are about 1 GtC per year now, so you would need a lot of reforestation to match just that, and then even more to offset emissions from other sources. Also we use the land for other purposes, like for growing food and for cities, so there is not that much land available for regrowth. Corinne

Hi both, and welcome to /r/science!

Corinne, what is the biggest area of uncertainty currently within the carbon cycle, and what are the steps (tech development/measurements/methods) being developed to address this? Also, what areas do you think will see the largest alterations to the carbon cycle over the coming decades?

Manoj, what do you think the chances are of keeping warming anywhere near the 1.5C Paris target - especially with the PDO/IPO seemingly switching to a warm phase and a reduction in industrially produced aerosols, especially in the east? Also, aside from the influence of ozone, could you please describe the main link between the stratosphere and climate in the troposphere?



thanks for ur question! on the natural carbon cycle, I'd say the biggest area of uncertainty is the response of the permafrost to warming. There is a lot of carbon stored in permafrost (~1700 GtC), and it's certain that at least some of the permafrost will thaw. What is not so well know is how much of the carbon (in CO2 and methane - CH4) that is stored there will be outgased to the atmosphere when the permafrost thaws. There is a lot of field work going on in this area, to actually measure the changes so the models can be better calibrated. There are also new measurements stations of atmospheric CH4 that try to detect changes at high latitudes. That's a very active research area. There are others of course. The Southern Ocean is another big store of carbon which responds to a changing climate. I hope to do some work there, I might even get to see the boaty mcboatface autosub! looking forward to that. Corinne

Addition from Manoj: A paper in Geophysical Research Letters suggests that the phase of the IPO could make a difference of about 5 years to when we nudge past 1.5C. Reductions in industrial aerosols also warm climate slightly, making staying within 1.5C more difficult- though reductions in aerosols such as soot would help to cool climate a little. Overall the chances really depend on emissions of greenhouse gases though rather than the IPO or aerosols.

To answer your other question- the circulation patterns of the stratosphere and troposphere can interact dynamically- so changes in the stratospheric circulation associated with climate change could have an additional indirect effect on tropospheric weather patterns, such as the midlatitude storm tracks


Hi Corinne! I've always wondered this. Since you've gone over a bunch of different ways that CO2 is produced, what stands out as the largest producer and how can the average person help to lower the numbers?


Thanks. There is not one source that really stands out, but transport, buildings (for heating and cooling), and industry account for most of the emissions of CO2. Agriculture is a large source of greenhouse gases but more for CH4 and N2O and less so for CO2. The average person can help in many ways, through your own choices (drive/fly less and less far; smaller cars; careful with the heating/aircon; etc). Even better is to try and influence the people around you, friends and family and policymakers. Have a voice. Corinne

Hi Professor Le Quéré!

Recent work in the Southern Ocean with buoys by SOCCOM has revealed the ocean may in fact be a net source of CO2 (far from current consensus). I understand these results to be preliminary but what do you see as the broad implications of a Southern Ocean CO2 source? I ask because of your article in Science (2007) about sink saturation. I'm hoping to be accepted for doctoral study into measuring flux in the ocean and was excited to see a name in r/science I'm familiar with!



thanks for your question on the Southern Ocean! I look forward to seeing the SOCCOM results published. I think if indeed they show a CO2 source in the Southern Ocean this simply means that the balance of processes (biological expert versus vertical transport from currents) in the carbon cycle models of the Southern Ocean is not quite right. We would learn a lot from this so good luck with your doctoral study!

What are the best carbon capture methods? Ignoring the option of not emitting it in the first place.


For the moment the only functional method we have is reforestation. But I would say the one that has the most potential is bioenergy with carbon capture and storage (BECCS). The Bioenergy produces energy so that's a benefit, the carbon capture is already possible and used in the fossil fuel industry, and the storage seems to also be possible based on large geological formations. The other methods like iron fertilisation of the ocean (there is a post on this on the thread somewhere I'll answer in a few minutes) and enhanced weathering are more experimental at this stage. There is also Direct Air Capture (DAC) with chemical processes, which would be great if it worked and didn't cost a lot, but at this stage I'm very skeptical.

Can electric vehicles save the world or do the generating and transmission losses and battery production nearly equal out to an efficient high mileage internal combustion engine?


good question! electric vehicles can go a long way to reduce emissions. In fact to deal with climate change most of the car fleet needs to be electric eventually (2030 or a little later sort of timescale). How far the electric car is from an efficient internal combustion engine depends in part on how low carbon the electricity is. On the generation and transmission losses, I don't know the exact figures for electric cars but I suspect the carbon costs of those won't be far away the carbon costs of current cars. I'm less sure about battery production. Typically for other technologies the carbon costs of production are repaid relatively quickly.

Hi Corinne, how big a part does agriculture have to play in this and what are the main things to be done to work towards sustainably feeding the world?


At the moment, agriculture is responsible for about 10% of the CO2 emissions and a quarter of the emissions of all greenhouse gases (because agriculture is particularly intensive in N2O and CH4 (animal burps, literally)). For CO2, 10% is not so much but the problem is that this is a part that is difficult to reduce. So if we are successful at reducing emissions in other sectors, agriculture will become an increasing priority. There is a lot that can be done in agriculture to reduce emissions. Practices like low tillage, soil and waste management, precision farming, livestock health, are all helpful to reduce the emissions from agriculture. A diet with reduced meat also helps even more, as would the reduction of food waste.

Given the recent spike in talk about anoxic periods, as well as general CO2 concerns, is there a reason people aren't talking about oceanic iron-seeding any more?


Thanks for the question. There have been lots of experiments on fertilizing the ocean with iron to try and trigger a carbon sink in the ocean. I think as much as 15 experiments were conducted all over the ocean. They were super interesting. Not long after the iron was put in the ocean, massive blooms of phytoplankton emerged in nearly all the experiments. The phytoplankton fix the carbon in their cells just like trees do on land. However it seems like the carbon does not systematically sink to the deep ocean (which is needed to store it in the ocean for a long time), and when the iron fertilization stops the CO2 is thought to mostly return to the atmosphere. The experiments were too short to really tell the fate of the carbon, but it seems the logistics of this are untenable as a realistic means of fixing problems.

Hi both - thanks for coming on here.

My question is about modelling - it's an essential tool for turning our knowledge of the climate system into policy-relevant real world predictions, but also causes a lot of public confusion. How do you think we can help people to understand what is meant by the different levels of uncertainty, and how much weight they can put on different model conclusions?

On a related point - climate models have moved forward beyond all recognition over the past few decades. What do you think the next big challenge(s) in modelling is (are)?



Excellent question- The UN IPCC does frame its projections using uncertainty, and I think it does a good job, but then I'm used to dealing with the language that it uses. The vast majority of people though have never come across an IPCC report, so communicating uncertainty effectively relies on the news media (pretty sure there's a relevant xkcd about this). I also think that public understanding of uncertainty in science is a much bigger issue than just climate, so perhaps better education of uncertainty in science in schools might help? I don't know how much of this is done.

There are lots of challenges in physical climate modelling: explicitly simulating so-called convective systems in the atmosphere having scales of 10 km or smaller in climate models (rather than 'parameterising' them, which is representing their net effects). Representing ocean eddies (which have scales of 10s of km) in ocean models which include not just physical processes, but processes affecting the carbon cycle is another challenge. ...but both of these (and many other) scientific challenges are associated with technical/computational challenges such as running computationally expensive models, storing all the data, distributing the data to data centres (etc). These technical challenges need to be overcome alongside the more scientific ones.- Manoj

What is your opinion on the current goal to limit warming to 2 degrees C? I'm a geology student, and I've done some basic climate modeling that shows the earth would still warm 2 degrees even if we completely switched to clean energy tomorrow. (Modeling was done on GeoCarb)


thanks for your question. I suspect you are looking at very long timescales (>1000 years)? The 2 degree C limit normally refers to about a century, and that can be met with rapid peak in emissions and reductions to near zero in the middle of this century. Very challenging but not impossible, especially if we can develop BECCS to offset a bit of the difficult-to-reduce emissions (e.g. agriculture).

Are you optimistic about deforestation rates worldwide? Is it slowing at an acceptable rate?


thanks for your question. There has been a lot of actions to reduce deforestation particularly from illegal activities in the past 20 years, and that's good. However worldwide it's not so clear if deforestation rates are decreasing at the moment. There is conflicting evidence from the satellite data (some of which suggest unchanged rates) and the ground statistics (which suggest decreasing deforestation). So I think there are still massive efforts to be done. Also the increasing demand for biofuels is causing pressures on forests and has to be dealt with very carefully. There is a lot to do! On the good side, there is regrowth in many places from land that have been abandoned and big management programmes in China, which offsets some of the deforestation. Next we also need to look at forest management, to do this sustainably.

Are there any countries or governments that are tackling climate change right that we should be looking to emulate?


Many countries do a lot to tackle climate change but I can't see one that shines as a real example across the board. Most countries where emissions have been reducing for a long time have laws or long-term policies with tangible targets (for example the climate change Act in the UK with a target for 2050 and a similar law in Sweden). These laws force governments to set targets and to devise measures to meet them, even when governments change. As a result the emissions are decreasing for now in these countries, but the efforts need to be maintained in the long term. One of the most important element is to have a cross-party commitment on tackling climate change, so that climate change is not a political agenda but just an agenda that you can address with the tools that you chose whatever your political party.

If plants require Co2 to live wouldn't they grow bigger if there was an increase of atmospheric Co2?


Yes!! and many are growing bigger indeed (the 'C3' plants). Growing forests absorb about 25% of the CO2 emitted to the atmosphere on average every year. Forests are one of two big carbon 'sinks' (the other is the ocean). The growth is not infinite though. CO2 triggers growth for a while but it stops when other nutrients or water run out, or just when the plant has reached its maturity (also the 'C4' plants don't react to CO2 so much because they have CO2-concentration mechanisms). The plants also react to a changing climate in ways that make the carbon sink on land less effective.

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