Dr Chris Brierley’s talk at the meeting on climate change, 16 November 2019

Public meeting on climate change, 16 November 2019

 How the climate evolved in the past and how it will develop in the future

Dr Chris Brierley, Associate Professor in Climate Change, University College, London

 Dr Brierley has two roles at UCL. One role is as a researcher, using climate models to simulate the climate of six thousand years ago, when the Sahara desert had vegetation right the way across it. Then the Earth’s orbit changed, the  vegetation collapsed, and the people living there migrated into the Nile valley, which sparked off the Egyptian civilisation.

His other role is as a lecturer, talking to and teaching students.

At the public meeting, he structured his talk around some of the things he’d done in the previous week, and how they related to climate change in the broad sense, to give a broad perspective.

For example, last weekend he went to see the film The Aeronauts, a story about a balloon ascent in the 1860s, when we really didn’t know much about what the atmosphere was, to find out more about the weather. This reminded Dr Brierley just how hard it was to get science information then, compared with today when he could sit in front of his computer all day. Then, they had to go up in a balloon and discover some fairly fundamental things about the structure of the atmosphere, and it was a very dangerous occasion.

To be more precise, the average temperature between 1850 and 1900 is often used by the international community as a definition of the Preindustrial time, which is the baseline, against which many climate agreements are measured. For example, the Paris climate agreement that was signed in 2015 was aiming to limit warming to 1.5°, and at most 2°, above that preindustrial baseline.

The science community was asked, what is the difference between a one-and-a-half degree world and a two-degree world, a thick textbook was produced; and one important thing that emerged was, what exactly was the preindustrial climate?.

So one of the things he did this week was to discuss with his colleague Ed Hawkins, who’s writing the next, more formal, assessment, the sixth assessment of the Intergovernmental Panel on Climate Change (IPCC), and they want to quantify just what exactly is the difference from that 1850-1900 period. That period is when we first had a global network of thermometers, and so we can really know what the temperature was. And the temperature during the period 1860-1900 turned out to be  0.1° ± 0.1° warmer than the slightly stricter ‘preindustrial period’, of round about 1700.

His first real lecture on Monday was talking to his first year students, to explain what the cryosphere was. The cryosphere is the ice sheet, the sea ice and the snow cover, and it is the most depressing lecture that he ever has to give. Because in saying what it is and where it is, you have to show observations of it, and this component of the Earth’s system is the one that is changing the most. And certainly on his slides, he has the sad note that by the time these students – who are about 19 or 20 – by the time they’re his age, it is expected that there will be no summer sea ice in the Arctic. And that is not a happy message.

He felt that his task at some point – and if he keeps on with his career, with maybe another thirty years of lecturing – his task in talking to geographers will not be to explain to them the science of climate change, but rather to explain to them a historical perspective of why we didn’t act fast enough, to deal with it, and why we bequeathed to them the changes that are going to come, and the changes that have already come.

He remarked that he probably has another thirty years left in his career, and at some point while he is still lecturing, he will have to explain to his students the historical perspective of why we didn’t act fast enough, and why we bequeathed to them the changes that are going to come, and the changes that have come.

There are two responses to looking at the future of the cryosphere, and looking at the future of the climate; they are defined as mitigation, and adaptation.

Mitigation means dealing with the cause of climate change, in other words, not putting any more stuff into the atmosphere. Nearly all of the scenarios described in the IPCC assessment show that once you get past about 2070, instead of having carbon dioxide emitted into the atmosphere, they are sucking it out. You can do that by planting forests, or by burning biomass to get energy and then capturing the carbon – you don’t let any of the carbon go into the atmosphere, and you put that carbon back down into the earth, and you sequester it away.


The carbon already in the atmosphere has committed us to some future warming, so the other side of our response is adaptation. That means how we adapt to the changes that we’re seeing already, for example, working out how much of the wildfires that have been happening in Portugal, in California and in Australia can be attributed to anthropogenic warming (i.e. warming caused by humans).

Adapting to these events involves changing our society, and changing the infrastructure within which that society works.

Within a community like this, we need to be thinking both about mitigation, and so cutting our carbon emissions, and we need to be thinking about how we can change our town and our community to better cope with the changes that are already in there.