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What will 1.5°C of global warming actually look like?





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Not much different… at first




Furthermore, some impacts such as sea level rise or species extinctions will lag behind the change in climate, simply because the processes involved can be slow. It takes decades or more to melt glaciers, so the input of extra water to the oceans will take time.

None of this should lull us into a false sense of security, however. While rising seas or biodiversity losses may not be obvious in the first year above 1.5°C, some of these changes will probably be already locked in and unavoidable.

The extent to which a 1.5°C world will see these other impacts depends on the still-uncertain level of “climate sensitivity” – how much warming occurs for a given increase in carbon dioxide. Higher sensitivity would mean even a small rise in CO₂ would lead to 1.5°C, so fertilisation and acidification would be relatively less important, and vice versa.

Impacts of staying at 1.5°C

There is a huge debate about whether limiting warming to 1.5°C is even possible or not. But even if it is, limiting global warming will itself have consequences. I’m not talking here about potential economic impacts (whether positive or negative). I’m talking about impacts on the kind of thing we are trying to protect by minimising climate change itself, things like biodiversity and food production.

In scenarios that limit warming at 1.5°C, net CO₂ emissions would have to become negative well before the end of the century. This would mean not only stopping the emission of CO₂ into the atmosphere, but also taking huge quantities of it out. Large areas of new forest and/or large plantations of bioenergy crops would have to be grown, coupled with carbon capture and storage. This will require land. But we also need land for food, and also value biodiverse wilderness. There is only so much land to go round, so difficult choices may be ahead.

So while the Paris Agreement ramped up the ambition and committed the world to trying to limit warming to 1.5°C, we should remember that there is much more than a single number that is important here.

It would be naive to look at the climate in the first 1.5°C year and say, “Okay, that’s not so bad, maybe we can relax and let the warming continue”. It’s vital to remember that at any given level of global warming, we have not yet seen the full impacts of it. But nor have we seen the impacts of holding back warming at low levels. One way or another, ultimately the world is going to be a very different place.The Conversation

Richard Betts is chair in climate impacts at the University of Exeter.
