Discussing the climate change evidence

The concept of climate change and global warming began to make headlines in the 1970s and scientists today largely agree that climate change is happening...

But what are the signs and the evidence, and what will be the consequences? Emily Shuckburgh, from British Antarctic Survey and the UK Government's Department of Energy and Climate Change, discusses...

Kat -   So, explain to me, what exactly is climate change?  What does it mean when we use these words?

Emily -   Well, as you say, we've been seeing signs of disruption to our climate system in the melting of glaciers, the decrease in the amount of sea ice particularly in the Arctic, in the rising sea level and in rising temperatures.  So, we've seen over the last century nearly 1 degree centigrade temperature increase.  When you take those different signals together, we see a collective picture of a changing climate and that's what we mean when we talk about climate change.

Kat -   So, I mean, we sometimes hear things when we get particularly savage winters.  People go, "Well so much for global warming."  But explain to me how overall the world can be warming, but the climate in different places can be changing in different ways.

Emily -   The last few winters, we've had a number of occasions when there've been particularly cold winters.  In the UK, there was one year recently when Heathrow was disrupted because of abnormal snow conditions for example.  But that was due to a shift in weather patterns at the same time as it was particularly cold here in the UK.  It was actually abnormally warm in parts of Canada.  So, whilst you can have different weather conditions due to shifting weather patterns in different parts of the world, what we're seeing overall when you average across the whole of the globe is a steady warming trend.

Kat -   So, you mentioned overall being able to see this warming trend.  What is the evidence that we have that the climate is changing?  How can we trust that this is really happening?

Emily -   So, I think the key question is, how do we know that humans are influencing this change?  And we have seen a steady increase in the amount of carbon dioxide in the atmosphere since the start of the industrial revolution.  The carbon dioxide levels are now about 40% higher than they were at the start of the industrial revolution.  And we know that that is predominantly through the burning of fossil.  And so, it's through that that we can link human activities to the change in the composition of the atmosphere.  We then know that the greenhouse effect kicks in. If you increase the amount of carbon dioxide in the atmosphere, that changes the energy balance of the Earth and results in warming of the surface of the Earth and they are the knock-on effects in terms of the disruption to the climate system. 

Kat -   So, we see sort of climate predictions where people say, "Well, it could go as far this or maybe just as bad as that."  Paint me a couple of pictures, maybe a sort of worst case scenario of how bad things could be and then maybe a kind of consensus scenario of where we think we'll be in maybe a few decades time.

Emily -   So, the concern is that if we continue emissions of greenhouse gases at the current rate then we might exceed 4 degrees temperature increase by the end of the century.  Now, what does that mean in terms of our daily lives?  Here's just one example - it might mean that we see up to 1 meter of sea level rise.  That increase in temperature has a significant knock-on effect, not just in terms of human lives, but then also on all ecosystems and critically, it also raises the risk of severe, abrupt, and irreversible changes to our climate system.  Another sort of example of how those temperature increases can affect everyday life - Uganda's top earning export is coffee and at the moment, large sections of the Ugandan countryside are ideal for growing Robusta coffee.  But if we saw just a 2 degree increase in temperature then that coffee production would be decimated.

Kat -   I guess as soon as the politicians in Westminster see it flooding and can't get coffee, they might start to pay attention.  But very briefly, can you explain to me a little bit - you mentioned CO2.  How can we project?  What are the projections for how much CO2 we can afford to release and I guess this is an issue for business about what we can afford to be burning in the near future to avoid these kinds of catastrophic rises.

Emily -   So, the science says that we can burn no more than a total of a trillion tons of carbon if we want to avoid going above 2 degrees temperature increase.  To date, we have already burnt 70% of our carbon dioxide allowance of that.  Now, if we look at the total current proven reserves of fossil fuels, the consequence of that science says that two thirds of our current proven reserves of fossil fuels are effectively unburnable if we don't want to increase our temperatures above 2 degrees. And 2 degrees is the level that's considered to be avoiding dangerous levels of climate change.

Kat -   And I guess briefly, that does have quite big knock-ons for businesses and how they're projecting in the future, where they're getting energy from.

Emily -   It does and just the current value of that unburnable carbon is about $20 trillion dollars.

Kat -   Dr. Emily Shuckburgh from the British Antarctic Survey.  Thank you.