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4 degrees C – an unavoidable catastrophe?

By Richard Betts

If global greenhouse gas emissions do not begin to decline in the next few years, the chances are that global warming will exceed the 2°C “guardrail” that the EU and UN aim to stay below. HELIX is researching the impacts of higher warming levels, specifically 4°C and 6°C. What would a 4°C or 6°C world look like, and when could these be reached?

If the world does warm by 4°C, this can be expected to have profound implications. Previous research shows that some areas could get a lot drier, while others a lot wetter. Many places will warm by more than 4°C, and indeed we’d expect more of the major heatwaves such as that which caused many deaths in India this summer. Also of course we’d be locked in to ongoing sea level rise due to melting ice and swelling of warming ocean waters. HELIX research is looking into these in detail.

As for the timing, the IPCC 5th Assessment Report gave a wide range of estimates of the speed of future warming. The different estimates arise from different assumptions on how greenhouse gas (GHG) concentrations will change, and differences between the various computer climate model simulations of how the climate responds to these GHG changes. For a scenario of high GHG emissions, the earliest time of reaching 4°C above pre-industrial was around 2070, and the latest sometime after 2100. In the most extreme case, 6°C is projected by 2100 although most models do not show this. If feedbacks are stronger or weaker than in those simulations, the timing could be outside these bounds – but evidence for these would need careful examination before we could be confident in this.

HELIX is also examining the communication of climate science. This is a crucially important issue, as our research has major implications for society, informing decisions on both the mitigation of climate change (whether / how fast to reduce GHG emissions) and adaptation (how to live with changes that we cannot – or choose not to – avoid).

Some might argue that the focus should be on worst-case catastrophic scenarios, leaving no room for doubt, in order to promote urgency in emissions cuts. It’s certainly easy to see why this might be tempting, as global emissions have continued to rise despite clear indications that unchecked climate change poses large risks.

This seems to be the case in a recent BBC Newsnight item, with the actor Emma Thompson interviewed in connection with Greenpeace protests against Shell’s plans for oil exploration in the Arctic. Ms Thompson spoke passionately and in no uncertain terms about 4°C warming by the 2030, and stated that “in a few years …. whole swathes of the Earth will become uninhabitable”. These statements do not reflect what the science actually says.

Does this matter? What’s the harm in a bit of exaggeration if it’s in a good cause? To my mind, there’s three reasons why it’s a problem.

Firstly, making wild predictions that don’t come true obviously harms your credibility. It’s the old “boy who cried wolf” story – he made up the story of the wolf, so when it eventually did come, nobody believed him. There was a wolf, but only later on. When the world has not become a barren wasteland within a few years, it will be easy for critics to say that the whole climate change problem has been exaggerated. It has not been exaggerated – at least not by mainstream science – but that will be easily overlooked when harking back to these claims.

Secondly, if people come to believe that catastrophic impacts are only round the corner, this could lead to wrong decisions made in panic. A lot is being done to make us more resilient to the climate change we’ve already set in motion – new flood defences, plans for reservoirs and water supplies, and so on. But these are expensive, and doing these too early could cost billions. And if people are scared into moving away from their homelands because they think it will be uninhabitable, this would only add to the existing refugee crisis, for no good reason.

Finally, even if the world does make major emissions cuts very soon, this will take time to filter through into tangible effects on global warming. There is already more warming in the pipeline which is unavoidable. Therefore anything projected for the next few years is already unavoidable. If “whole swathes” really will become uninhabitable “in a few years” then there is absolutely nothing we can do about it, however urgently we cut emissions. Whether Shell drill for Arctic oil or not, the changes for the next few years are already locked in. Emma Thompson’s apocalyptic vision is therefore one of despair, not something that can credibly be avoided through action, however drastic.

Fortunately, while Ms Thompson’s concerns are valid in the longer term, her timing isn’t supported by the science. Higher levels of climate change and the associated risks are further off than she fears, and hence could still be avoided. Whether we choose to attempt to do this or to try instead to live with the risks is a choice that the world needs to make. There are no easy options here, and such a choice is hugely important. It needs to be properly informed by sound science, communicated responsibly to the world.