Question: Do you think climate change is reversible or that we can stop it

Fabian Grosse answered on 30 Jun 2020:

Indeed a very big question, perhaps one of the biggest to modern societies. I am also NOT a climate scientist, which is important to bear in mind. But part of my work is strongly related to climate change, so I am familiar with SOME of the climate (change) literature. I know of three concepts, which I think need to be talked about in this context: (1) positive feedbacks, (2) tipping points, and (3) equilibrium states. And there are proobably more!
(1) One example of a positive feedback in the context of global warming is the so-called ice-albedo feedback of the polar regions. In other words, if the temperature increases, we have less sea ice for a shorter period of the year, and as a result the ocean heats up faster (because the relatively bright surface of the ice reflects much more of the incoming sunlight back into the atmosphere than the comparably dark ocean water). So this means the increase in temperature results in an even faster increase in temperature. Another positive feedback is the thawing of the permafrost in Siberia and Canada. The warming causes the thawing, which is expected to result in the release of large amounts of greenhouse gases into the atmosphere, which would again speed up the warming process. I am not sure to what extent this is already happening.
It’s important to note that these feedbacks are natural processes but we significantly amplified and them and brought them out of balance in a very short amount of time.
(2) Tipping points can be described as thresholds of certain quantities or conditions (like air temperature), which–when exceeded–can trigger chains of processes (like positive feedbacks) that will result in irreversible change and a new state of the climate system (or parts of it).
Scientists have been able to identify a few of these tipping points but I don’t know which ones exactly, and I also can’t tell whether or not some have already been reached or not.
(3) This leads me to the third concept: states of equilibrium. This doesn’t not mean that everything is the same all the time (we know, temperature in the UK changes between summer and winter and we can have a warmer summer in one year, and a bit colder one in the next one) but certain factors will vary around some long-term average every year and these specific conditions in the specific regions allow for certain plants to grow and animals (incl. ourselves) to live. If the climate system reaches such new state of equilibrium, it might be not (or less) inhabitable for us and many other species, while it might be more inhabitable for others. Some species are likely to go extinct because their natural habitats just vanish (e.g. the polar regions whose climate might be more subpolar or temperate in a few decades). However, once a new equlibrium state is reached, you may say that climate change has stopped. Yet, it will be very unlikely to be reversed then because the earth system has reached a new ‘stable’ state but with different environmental conditions than we have experienced in the past.

So, the answer to your question is really not easy. Personally, I think part of the changes we already notice are probably irreversible (like the decline in sea ice). And I wouldn’t know how we would actually be able to cool down the Earth back to temperatures 50 years back right now (but perhaps there are ways). Other changes might be reversible but they are likely to become irreversible if we–as a global human society–don’t act now.
And one way or another climate change will probably stop at some point: either because we manage to keep it below these critical tipping points or because we fail and it reaches a new stable equilibrium state. However, I am very concerned that such potential future stable state is not very livable for humans in large parts of the world, so we should do whatever we can to not reach these tipping points, and since we don’t exactly where these are (like at what temperature levels), we rather act sooner than later and with all ethical(!) means we have at our disposal.