Pessimism is a dirty word in climate policy circles. There are good reasons for this. Especially because while optimism can encourage positive change, assuming the worst can paralyze us and prevent us from taking action. But when it comes to climate modeling, a certain amount of negativity can be a good thing.

The Intergovernmental Panel on Climate Change is already working on various models and pathways to assess how to limit warming to 1.5°C and how to ensure that carbon emissions continue unabated or experience many possibilities in between. I use it to hedge my bets. These pathways are backed by thousands of scientific papers, tons of data, and the brains of the world’s climate scientists, but like all models, they are built on assumptions.

One of the key assumptions in the scenario of keeping temperature rise below 1.5°C is that the technology to remove carbon dioxide from the atmosphere will be rapidly perfected in the near future. This is not an unreasonable prediction, given human ingenuity and strong incentives to do so. But incorporating carbon capture technology into these models is like declaring that winning the lottery will balance the household budget. If you can’t reduce your spending to an affordable level, you better hope that a big prize is on the way.

As the two articles in this issue demonstrate, this is a dangerous approach. A detailed analysis of geological carbon storage plans shows that it is at least very unlikely, if not impossible, to meet the levels envisioned for many 1.5°C pathways. (“Our plans to tackle climate change with carbon storage add up”). The chances of winning the lottery don’t seem that high. On the other hand, we also received an unexpected carbon bill in the form of melting Arctic permafrost, releasing more greenhouse gases than previously accounted for. Frozen soil is now a major net source of greenhouse gases (see “Frozen soil is now a major net source of greenhouse gases”).

While these revisions in our understanding of climate change are entirely expected and to be welcomed, they do signal that the challenges we face over the next decade will only get more difficult. . Rather than narrowing down climate models until the numbers roughly match the 1.5°C goal, perhaps it would be better to take a more pessimistic outlook and accelerate efforts to limit the damage.