Could the current climate change events cause long-term problems in the viability of Earth to sustain life?

Question

There are a lot of reports on the consequences of climate change for the relative short term. From what I understand, in the next 100 years or so, we will face:

• global floods of coastal areas, causing large-scale migrations;
• desertification of desert-adjacent regions, leading to more migrations and less arable land;
• more and longer periods of drought and heatwave, leading to failed crops and hunger epidemics;
• changes in local climate, leading to changes in biodiversity and possibly introduction of pathogens in areas that before were inhospitable to the carrier;
• ...

I might be totally mistaken here, but while these things are definitely cause for serious concern and good reasons to take action, they don't seem like they could cause the end of life on Earth as some people claim, or even the extinction of Humanity. I'm fairly sure that even though loads of people might die due to the consequences of climate change, humanity as a species would probably survive. I might be wrong though.

Could climate change lead to the extinction of humanity?

Answer 1

There is one scenario in which climate change could render the Earth inhospitable to life in general, which would be a runaway greenhouse effect. In a runaway greenhouse effect, the Earth would get so hot that the oceans start to evaporate, adding more water vapour (powerful greenhouse gas) to the atmosphere, which will make it hotter yet, until Earth ends up like Venus. However, the current scientific consensus is that a runaway greenhouse effect as a consequence of anthropogenic global warming is not possible.

Life in general will almost certainly go on, and most consider it unlikely that the survival of humanity itself is at risk as a direct consequence of climate change. Many other species, however, will likely disappear, as has been widely documented in the scientific literature. As an example, complicated ecosystems depend on coral reefs, and as things stand, there may not be any coral reefs left by the end or even the middle of the century. This will be disastrous for significant subpopulations of humanity (I've heard in a talk last week than 400 million people depend on fish supported by ecosystems around coral reefs), but it will not by itself cause the extinction of mankind.

Answer 2

Depends on the further actions humanity takes. If we keep on pumping green house gases into the atmosphere, survival will become significantly harder. Sure, we most likely wont be able to create a Venus-like atmosphere, but as of today we simply do not know, what tipping points in the climate system we might go beyond.

Actually I am more concerned by the steps humanity might take in the wake of climate change. On the one hand, all out war is a possibility, diminishing our capabilities to cope with the consequences of climate change. On the other hand, we might be so "brilliant" as to dabble in geo-engineering - and really fuck up the climate system beyond repair. Imagine someone like Trump fighting climate change instead of imigration - the consequences could be catastrophic.

Specific forecasts are out of the question - but basically, I think there is a very slim chance we as a species could go extinct - alongside most of the other animals. Our current consumption of ressources definitely wont be possible anymore.

Answer 3

100 years is not very long-term at all. The added CO2 will not miraculously disappear after a century, but will go on warming the planet. (And that's just assuming that humans stop burning fossil fuels now.) There are all sorts of feedback effects that will come into play at some point, if they haven't already.

For one example, a lot of CO2 winds up dissolved in the oceans, and the solubility is inversely proportional to water temperature. As the ocean warms due to human-generated CO2 in the atmosphere, it becomes less able to serve as a CO2 sink, and eventually would release some of its existing CO2, causing further warming. The ocean mixing time (between surface and deep ocean) is on the order of 1000 years, so whatever is set in motion today keeps on happening. The warming ocean might also trigger the release of methane clathrates: https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis

However, we don't really have to theorize that much about the long-term effects, since we have a reasonably close parallel from Earth's geologic past: the Permian-Triassic extinction event: https://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_event One leading theory for the cause of this is that major vocanic eruptions (the Siberian Traps) took place in an area of coal beds, setting them on fire. This of course added lots of CO2 to the air, just as human use of fossil fuels has.

So the hypothesis is that the current warming (and future warming that is already "baked in" by the already-released CO2) will trigger unstoppable feedback effects. Not quite a runaway "Venus Effect" (that's probably impossible on Earth), but one that causes mass extinctions.

Some people think that humans would survive those mass extinctions. I doubt that*, myself. Too many people live lives divorced from the natural world (thinking for instance that food comes from supermarkets & fast-food joints), and so fail to appreciate just how strongly human survival depends on the existence of the global ecosystem.

*Of course this is opinion. The only way to test it (other than computer models) is to perform the experiment, which is analogous to checking whether a gun is loaded by pointing it at your kid and pulling the trigger :-)