American Geophysical Union AMA: Hi Reddit, I'm Piers Forster, I am here to talk about what caused past global warming and what will happen in the future. I am currently Chair of Climate Physics and Director of the Priestley International Centre for Climate, University of Leeds, UK. Ask Me Anything!



Do small countries going green make a difference, or is it all on big countries who are leading in pollution?


In terms of climate change – the big emitter countries share most of the blame for sure (China, US, Europe, India etc.) but more and more countries such as Nigeria are becoming significant emitters. And the world needs to get all emissions of CO2 to zero to prevent further warming , not just reduce them. So every sector and ountry has a role. Also when you break it down – the top 10% of a countries population are typically responsible for over half the emissions, so it is really the wealthy of the world that drive climate change

We all know nuclear energy has the least impact on climate and the most contained carbon footprint. Yet there seems to be a movement away from it. How do you feel about the choices developed economies are making today with respect to their energy mix ratios?


Today, they have really hit climate targets by moving from coal to gas. Renewables have helped, but I fear that the gas move (fracking in US, importing gas in the EU) is a short term fix. And I know my own country (UK) keeps wavering on longer term plans. Biomass is another 10 year option. Renewables can grow of course but take space. I see either a renewable/nuclear future and/or one that sees lots of carbon capture of fossil fuel and biomass. No country really tries to tackle demand

What do you think the timeline is for the development of reliable decadal-scale climate forecasts? Century-scale projections are useful for certain applications, but models synchronized with current observations and internal variability would be more useful for management purposes.


Great question. We have a project looking into this just now. It depends a little on what you are trying to forecast. I’d say it maybe only 5 years away for global average temperature. But we might have to live with the fact that we may never be able to get regional info. We don’t know how much of decadal ocean variability will ever be predictable. Some of it will be, some of it won’t. If a large fraction isn’t that predictable we might always be struggling… .. Of course if we to continue to emit 40 billion tonnes of CO2 – the human signal quickly dominates, making prediction easier!

Thank you for taking the time to do this!

With your expertise and experience. What is one staple and concrete fact that you'd present to every naysayer? I was actually in a debate amongst a few friends and they mentioned that the earth is always wanting and cooling. They also used the ice age as an example.


A string of facts: CO2 is a climate warming gas (measured in the lab); we have recorded its increase in the atmosphere, since the 1950s directly; we know this increase is down to us (we can trace its isotopes to fossil fuel burning). We can calculate is warming effect from the laws of physics. This estimate matches the observed warming. No other credible explanation of the observed warming exists; and p.s. 4 independently created estimates of the observed temperature increase agree with each other

Thanks for doing this!

Can you give your best estimate on how long it will take for naturally occurring emissions (for Arctic methane release and permafrost melt as well as failing CO2 sinks) to reach 50% of total global CO2 and CO2e emissions and what if anything could be done by that point to slow/reverse the warming?


No - and it might not even happen - more methane currently coming from tropical wetlands - and no one knows really why rather than permafrost. Need to research!!

This is a question that becomes increasingly relevant in America, especially under the current administration. What can American climate organizations do to stop politicians from making climate change a political issue rather than a scientific one. Also, what can average citizens do to counter this problem.


Great question and one I spend a lot of my time thinking about. I think we as scientists need to spend more time talking to republican/conservative audiences. And separate the evidence that proves human-induced warming from society deciding what action to take. We also need to talk in language they understand: opportunities for the economy, risks for investments/jobs/growth/ energy independence

Good luck - tell me how it goes!

Hi Dr. Foster, thanks for doing this.

Have any efforts been made to run CMIP5 class climate models (or others) in an effort to minimize 21st century warming (perhaps its even possible to induce cooling some parameter regimes) under the constraints of a 1850-2000 hindcast, just to see what it would look like?

It seems to me that this kind of work is necessary to settle once in for all whether models really have too many tunable parameters to make reliable projections. I know people check sensitivity of climate sensitivity to various parameters but I haven't seen anyone actively try to produce the coolest 2100 temperatures while still matching the observational record.


Many CMIP5 models can easily get 20C cooling. They do it by changing the way aerosol particles (mainly from SO2) interact with cloud. Those with a large aerosol-cloud cooling effect, cool more than the greenhouse gases warm. But in no model - does the 21C cool as SO2 emissions from coal burning are all expected to decline. I don’t know of exactly the experiments you seek. But some CMIP5 models with low climate sensitivity, give low rates of warming, so they have almost done your experiment by accident – see Figure 12.8 of IPCC WG1 report

Where should I be buying property so that my children can live through this?


Somewhere on a hill, in a temperate part of the world. Home grown food that doesn't depend on snow-melt for water. But in reality and as always, you'll likely be fine growing up in a rich country with good infrastructure and government - its the poor and badly governed that take the brunt and ironic they didn't cause it

In terms of solutions, isn't the overall effect that consumers have on global warming minuscule compared to manufacturing, energy, and agricultural industries? With waste production, people can recycle and reuse old containers, but that effort is a drop in the bucket that is quickly being filled by the aforementioned industries. My question is, can consumer habits truly change the trends in global warming? If everybody stopped eating animal products (the single largest source of greenhouse gasses), it would certainly make a substantial difference, but that will never happen. The most realistic scenario is that even if a growing number of people in the United States and Europe reduce their consumption of animal products, that reduction will be negated by the expanding middle class in developing countries. The question being, again, is individual responsibility in changing habits going to have any effect?

Edit: for clarity, I do believe that veganism and a priority towards waste-to-energy practices should be integral in our overall environmental policy, both as individual consumers and as commercial or political bodies.


This does have an effect and is cheap - in US and UK food waste accounts for around 10% of our country's emissions a vegetarian diet could cut out another 10%. To get a 20% cut via technology would cost billions - whereas these changes save you money!

What do you make of cycles in the obliquity of earth's axis as explained here:

From what I see, these researchers claim that only trends in obliquity correlate with past climate shifts, they do not see a causal effect of CO2.


This is well known. CO2 changes did not cause the glacial cycles, but changed as a response to them (so was a feedback). This feedback amplified the effect of obliquity changes, much like the water vapor feedback today amplifies the effect of our CO2-induced warming (but on much longer timescales)

How much impact does personal change of lifestyle have? I would think a lot since without consumers large industries and corporations have no reason to do anything.

Over the months I have read scientific research and compiled as short as possible list of personal changes every person can make. Can you please look at it and see if I'm mistaken about something.


  • eat less meat, dairy, and other animal products (none is the best)
  • eat less industrially produced food, less processed food, less packaged foods (for example, bottled water uses energy to be packaged and refrigerated, and produces plastic waste so drink tap water)
  • eat proper portion sizes
  • remember that food which pets consume also has impact on the environment so adopt don’t shop to discourage their production, and choose pets that are herbivores


  • drive less, cycle and walk as much as possible, avoid flying
  • use efficient lightbulbs, turn the lights off when you're not in the room
  • Unplug devices when not in use (to simplify this you can get remote controlled electrical outlet, some are very cheap)
  • insulate your home, don't warm or cool the rooms more than necessary
  • criticize and complain about large buildings like malls that warm up or cool down the air too much
  • forgo living in a single-family house in favor of apartment-style housing. (that way more people get to live on less land, sharing walls is more energy efficient, commutes are shorter etc.)
  • buy solar panels
  • don't be afraid of nuclear power plants


  • avoid items with too much packaging
  • don't buy more than you need (but for items that you are certain you will use and can last for a while buy in bulk to avoid extra packaging)
  • buy recyclable items (q-tips with paper stick instead of plastic, bamboo toothbrushes, etc.)
  • recycle
  • avoid single-use items (don't use disposable cutlery and cups e.g. bring reusable tumbler to Starbucks, disposable wipes, disposable plastic bags, if you are menstruating use menstrual cups instead of pads or tampons, etc.)
  • contact manufacturers and complain of excess packaging


  • don't flush the toilet when not necessary
  • don't throw anything in the toilet except bodily fluids and solids, and toilet paper (no cotton pads, no q-tips, no floss, no tampons, no cigarette butts, no paper towels...)
  • turn the water off while you are lathering, brushing your teeth etc.
  • cut down on showers and baths
  • don't water your lawns, try to plant local plants that don't need watering


  • Encourage others to adopt sustainable lifestyle (feel free to share this list)
  • Donate money to environmental charities
  • Be careful who you vote for, pressure your representatives and politicians
  • Look into buying carbon emission offset (this is the only point on this list that I haven't researched yet, so I'm not sure)

Great list - I'm impressed. What to prioritise depends on where you live - it temperature and how green your energy supply is. ie. with renewable energy you don't necessarily need eco lightbulbs...

The poleward shift of storm tracks was predicted by models several years before it was actually observed and it seems to be only replicated in models that have a climate sensitivity of >3°C. Does this suggest a higher ECS or rather issues with modeling the response of storm tracks?


good Q - maybe both. low estimates of ECS look increasingly less credible for vanity of reasons - but high resolution needed for correct storm track response

1) How do we know for sure the temperature variation is human related? Do we know this answer from data or from speculation?

2) Should we has humans control the climate? Should we be fighting the human induced climate change or should we focus on being able to do more than that, since any major cataclysm could whipe us out.

3) It was the continue release of gases that created the ozone layer problem, isn't the continue leeching of energy from the environment something we should also be worried about? Specially when everyone is starting to do it on a massive scale?

Thanks for your time!!


1) We know from data: see my answer above

2)Not until we know more and have a world government. Controlling climate somewhere may harm people elsewhere. Like cloud seeding causes rain to fall on you - but not your neighbor - they may not like this! 3) Ozone hole gases are not really emitted anymore and ozone layer is recovering - a great news story - so we can fix things. Other problems are an issue still but we can improve our environment with good science-led policies

What percent of climate change is man made?


Yes, our best esimate is that 100% of the warming since the 1950s is manmade. We also likely caused warming before then, but we are less sure as to fraction

This AMA is being permanently archived by The Winnower, a publishing platform that offers traditional scholarly publishing tools to traditional and non-traditional scholarly outputs—because scholarly communication doesn’t just happen in journals.

To cite this AMA please use:

You can learn more and start contributing at


Thanks man/woman!

Based on your experience with society, money's influence on it, short term reward vs long term reward, how people view nature... what is your personal opinion on how the climate crisis will develop? Can people go minimalist and vegan and save our planet? Or are we all so guided by the average american dream of more money, more things, that colonization of space is our only hope?


Going vegan is a great choice of course but for everyone on the planet and breeds the view of a liberal elite. Its a global problem, so you need a solution that works for everyone. One day we may all live in a world like Scandinavia and there is talk that we have reached "peak stuff". But the Swedes fly around the world for experiences, so their emissions haven't dropped. So are think we are really looking at national sale technological solutions. And eventually a Dyson sphere?

Thank you for doing this AMA,

I recently watched Cowspiracy, a documentary on how the world’s leading environmental organizations are too afraid to talk about animal agriculture as being the primary reason for climate change (let alone numerous other problems) as encouraging more environmentally sustainable diets and apparently repels 'supporters' of these organizations. Instead of focusing on the fact that it takes ~660 gallons of water to make a hamburger, or ~4 gallons of water for a gallon of milk, these organizations encourage us that the transportation and domestic sectors are the primary reasons for climate change and other environmental ills. They tell us to fix leaky faucets and to do other small tasks as people do not like larger commitments.

In your opinion, what do you think must happen in order to spark this commitment? A grassroots movement? Education? More radical journalism which exposes the animal industry? Are we too late?


Eating meat infrequently works pretty well too

Is there a point of no return? If so, is it likely to be the end of human life or is it more likely to be mass devastation and everything sucks but we'll find a way to cope?


I don't think humans are under threat - we know enough about adaption and survival - just hard to sustain 7+ billion of us

What can you tell us about the Paleocene-Eocene Thermal Maximum (PETM) in relation to current climate change? Do you have a specific theory/hypothesis for the cause of the PETM that seems most likely to you? Thanks.


Sorry, I am not expert enough. I hear colleagues talk about competing theories but am not well informed enough to judge..

Is there any realistic expectations in Coccolithophores or other natural (phenomenon) to clean the ocean or air of co2? I've read Cocc. are potentially harmful as well, because they thrive on co2, but also produce a little and may affect the upper layer of the ocean.

With all the increased research into making artificial cells/protiens/ect is it realistic to think we could make something close to Cocc. but...better? I thought I read that that fake protein 'grows'. Can co2 even be converted (or w/e) on a large scale to another molecule (or w/e) or energy for an artificial cell that use to duplicate itself (mitosis..idk?) or grow.


lots of ways to covert CO2 from atmosphere into stored CO2 - but takes energy and the scale is huge- we emit 40 billion tonnes - no way to pay for it at moment

Hi Piers! Many thanks for doing this.

I also lead an interdisciplinary centre looking at climate solutions, and I would welcome a discussion of ideas on possible solutions. Does solar geoengineering or large-scale carbon capture and storage have legs? Where should we concentrate research effort? Any whacky ideas we should look into?

I think that its likely changing the climate maybe an easier challenge that changing human nature, at least in the short term, and therefore one of the most promising routes out of the climate challenges we are facing is a capitalistic one. If something is good (or less bad) for the planet and makes financial sense it generally seems to appeal to those on both sides of the political spectrum.

With this is mind, are they any avenues which you feel have potential to re-work markets while favouring the environment?

Two areas I am interested in are Carbon capture with manufacturing and hemp!

In the last year or two I have seen there are some recent developments in terms of cost effective carbon capture from the atmosphere, but also some talk about how carbon fibre may be carcinogenic and not ideal to use as a manufacturing material. I would be really interested if you have any thoughts or ideas on this subject? Sometimes people mention that the ideal carbon capture and manufacturing concept already exists in the tree, which is of course true, but not a solution to our problems as the capital yield at present for woodland is too small to be valued enough to keep around it seems. Carbon fibre seems like a magical material due to its strength, versatility, and recyclability. I cant help thinking of all the hard waste in landfill that could transition to being carbon based.

Regarding hemp, there are not many developments in the last number of decades to ease production that I am aware of. The blocker for using hemp for clothing and paper (in an innumerably more ecologically friendly way than woodland) has been / is largely political. The tide seems to be turning at present and de-regulation of industrial (and other forms) of hemp in various nations. Have you performed (or are you aware of) any research of moving away from cotton and wood pulp and its effects on the environment? Any other thoughts on this area? (I know in the UK a university in North Wales have been looking at strains for cultivation in colder climates which could see a growth of the industry again here).

Great to hear any thoughts you have on the above!


interesting... Any carbon put into long lasting products helps but don't know specifics - had a student looking at different biochar and all feedstocks were similar in behaviour. Re market - I think it can work when coupled to regulation. i.e. if you regulated that said all fossil fuel emissions must be captured - the industry would do this within the market

Will planting more trees reduce the carbon in the atmosphere? Also why does no one talk about methane, when methane is much more harmful than carbon dioxide


methane warms more per Kg emitted but much more kg CO2 emitted

How much can one bad country (e.g. USA) cause damage for other places (e.g. Australia, Europe, Africa...)? Assuming everyone goes green except USA


US if goes bad- could add up to another 0.5 C (1 deg F) global warming by 2100

How comfortable are you with the climate debate being used as a political cudgel?


prefer it to be apolitical for sure

What do you think the future implications of climate change will be on humans in the next 50 years?



Depends where you live but warmer with more intense rainfall for all - 1-2 deg C warmer on average and rainfall intensity ~10% heavier at peak times.: hard to avoid

Are there any prospects for reducing the carbon in the atmosphere? By this I mean, does science foresee a way to "use" the carbon to our benefit so as to reduce and perhaps reverse the effects of climate change. If so, will we be able to essentially control the Earth's climate?


way too much is emitted to "use" - 40 billion tonnes per year

we are seeing temperatures climb in areas like the middle east and the Indian subcontinent dangerously high on a regular basis these days.

Do you think geographical areas that are currently being inhabited will be abandoned in the near future due to climate change? which areas?


low lying countries will definitely evacuate - we need to build cities differently across Middle East and India - but may need to leave

Thanks for the AMA!

Have you found/noticed any technology that would positively impact/reverse the damage caused from various pollutants?

Or what small things can the individual do to help out in present times?


There are some great answers above

If humankind were to stop polluting the Earth altogether immediately, how long would it take Earth to recover its CO2 levels to pre-industrial age?


it falls to ~halfway there over 50 years, 60% there by 100 years or so - but takes many 1000s of years to return

If a very large volcano erupts would the dust particles reflect the light and lower the earth 's temperature?


Yes - for 2-4 years only though -then they would pop back up

What can we do, as individuals, to work towards slowing the effects of global climate change


There are good answers above - by others!

Additional Assets


This article and its reviews are distributed under the terms of the Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and redistribution in any medium, provided that the original author and source are credited.