There has been a huge amount of worldwide media coverage following the weekend’s announcement of a globally agreed deal to try to limit global warming to 2 °C or less. Here Professor Stephen Belcher, the Director of the Met Office’s Hadley Centre for Climate Science and Services, discusses some of the scientific questions raised by the agreement.
At the heart of the Paris agreement is the aim to hold “the increase in the global average temperature to well below 2 °C above pre-industrial levels”*. Why 2 °C? Because global governments have previously agreed this is an achievable target which could reduce some of the most dangerous impacts of climate change – such as melting of ice in places like the Greenland which would cause large scale sea level rise.
The agreement went even further, however, by saying efforts should be pursued to “limit the temperature increase to 1.5 °C”. This is a more ambitious target, especially given news from the Met Office in November that the world has reached the 1 °C above pre-industrial marker for the first time this year.
It raises some interesting questions for scientists as to how we can achieve this: how much do we need to cut global greenhouse gas emissions? How quickly do we need to make those cuts? What else might we need to do to be able to keep warming to 1.5 °C – for example, would we need to develop technologies that actually remove CO2 from the atmosphere? If temperatures overshot 1.5 °C and then reduced to 1.5 °C, would sea level also overshoot and then reduce?
To answer these questions more precisely will require scientists to get an even more detailed understanding of how sensitive our climate is to CO2 and other greenhouse gases.
Key to this will be improving understanding of what we call ‘Earth system feedbacks’. These are natural feedback processes which could either increase or decrease the amount of warming we might expect in response to a given amount of greenhouse gases. For example, we know that there are stores of greenhouse gases ‘locked away’ under frozen ground (permafrost) in some parts of the world, such as northern Russia. If that permafrost melts due to climate change, the gases would be released – which could further increase warming.
Scientists around the world are already working on providing answers to these questions by developing a new breed of ‘Earth System Models’ (essentially complex simulations of our planet run on powerful supercomputers), which take more of these feedback processes into account, and so will help inform planning of emissions to achieve the warming targets agreed in Paris.
Whether we limit warming to 2 °C or 1.5 °C, it’s clear we can expect some further change to our global climate over the coming decades. Research shows us that this will lead to some impacts and it’s vital that we understand in more detail what this means at a regional and local level.
For example, research tells us that some parts of the world can expect more extreme weather – including heat waves and increases in extreme rainfall. For those planning everything from future homes, to flood defences, to vital infrastructure, the detail on what to expect is essential.
Again, these are questions which science is already working to answer by harnessing new research and ever more powerful supercomputing technology. At the Met Office, we’ve published papers showing that we can expect more intense summer downpours for the UK in future – which raises the risk of flash flooding. We’ve also shown how the chances of summer heatwaves in Europe have dramatically increased.
There’s still much more work to do in this area and it will be vital that the information generated by this research is presented in a way that allows everyone to make informed decisions about how we can become more resilient to our climate – whatever changes we can expect.
*There’s a lot of scientific debate about exactly what ‘pre-industrial levels’ means and how you would measure that, but here we use the average of temperatures during the period 1850-1899 as our representation.