The problem in my view, is that climate change could, if severe enough (say >3.5 degrees before 2100) become a "universal stressor", increasing the probability of various risks that in turn make other risks more likely. For example: economic stagnation, institutional decay, political instability,  inter-state conflicts, great power conflicts, zoonotic spillover events, large and destabilizing refugee flows, famine, etc. Every item on this list is made more likely in a warmer planet, but also made worse, because we will have fewer resources to deal with them. 

Each of these adverse events also increases the risk of other adverse events. So even if CC only increases the risk of each event by a small percent, the total risk added to the system could be considerable. 

With regards to the worst risks, this becomes even more problematic. Consider a nuclear winter scenario. That is pretty bad. But a nuclear winter scenario in combination (partly caused by) with a severe climate crisis is much worse (since CC will affect many countries that will be spared from NW, but also because countries suffering from CC will have fewer resources to help refugees etc).  

Now consider the added risk that a zoonotic spillover event might happen. This is also made more likely by CC. But in the case that we combine social collapse due to CC with zoonotic spillover it becomes more and more difficult to see a path from there to recovery. 

I have a paper from a few years ago arguing a similar point. https://iopscience.iop.org/article/10.1088/0031-8949/89/12/128005;jsessionid=7EACB368D908AD6B0EC00F6688E725DD.c2.iopscience.cld.iop.org#metrics 

From the abstract: 

This article argues that this research program [longevity treatement] is much more risky or less beneficial than its proponents argue. In particular, they tend to underestimate the concerns associated with the potentially drastic population growth that longevity treatment could cause. The ethical benefit often ascribed to longevity treatment is that such treatment would add more subjective life-years that are worth living. However, in light of contemporary environmental problems, such an increase of the human population might be reckless. Drastically reducing fertility to reduce risks associated with environmental stress would make the benefits of such technology much less compelling.

Send me an email for the pdf if you are interested. 

I have an article on this topic from last year.

Highlights

•Active SETI assumes that alien languages can be translated without context or meaningful interaction.

•According to prominent theories in the philosophy of language it is impossible to translate without context or interaction.

•The impossibility of communication between humanity and an ETI has important game-theoretical consequences.

•The failure of communication cause a “Hobbesian Trap”, where players are drawn to a risk-dominant equilibrium.

•In light of this, advertising our location to ETI is reckless.

https://www.sciencedirect.com/science/article/pii/S0016328718300405