In this first module, I want to talk about why a few
2:16degrees of extra warming can have such big, and some cases,
2:20scary impacts.
2:22Our natural world is already responding to the relatively
2:26modest warming and climatic change that we've had so far
2:30over the past century.
2:33This gives us a window on our future.
2:36Humans are the most remarkably adaptive creatures that have
2:40ever evolved.
2:42Our species is capable of changing our environment more
2:46than any other.
2:47But this very ingenuity is putting our environment and
2:51our very civilisation at risk.
2:54So let's see simply start with some facts.
2:57Our insatiable desire for energy to support our
3:00civilisation has had some really unintended
3:04consequences.
3:05We have found that one of the best ways of producing energy
3:09is to use the fossilised bodies of plants and animals
3:13laid down in the Earth's crust as carbon.
3:16In using this energy source, we have been redistributing
3:20this carbon from the Earth's crust into the atmosphere, and
3:24this is having big impacts.
3:27These consequences mean that not only is the world warming
3:31up, but our rainfall patterns are changing.
3:35Along with this, there are physical changes to the
3:37Earth's surface.
3:39Glaciers and polar ice caps are melting
3:41faster than ever before.
3:44Sea levels are rising, and the very chemistry of
3:47the ocean is changing.
3:50So where to now?
3:51How fast will these changes occur in the future?
3:54And do they really matter?
3:57To even begin to start answering these questions, we
4:00need to make some very important assumptions.
4:03How fast will our population grow in the future?
4:07How many of our resources will we consume, and at what rate?
4:12How will we produce our energy?
4:14All of these things affect how much greenhouse gas we put
4:18into the atmosphere, and therefore, affect our climate.
4:22So let's begin by looking at two very different potential
4:26pictures of our future.
4:29If we continue to use fossil fuels as our main energy
4:33source, and the rate at which we emit greenhouse gases into
4:37the atmosphere stays on the same path as it has over the
4:40past decade or so, and the world's population continues
4:45to grow, then carbon dioxide levels in the atmosphere by
4:492050 are predicted to be about double what they were before
4:54the Industrial Revolution.
4:55That is, about 560 parts per million.
5:00And if we carry on the same for even longer, by the end of
5:04the century the concentration of CO2
5:07will have about tripled.
5:10This is often called a business as usual scenario.
5:14You CO2 does get to double what it was in preindustrial
5:18times, global average temperatures could be between
5:22about 2 and 4 and 1/2 degrees above that time.
5:27Have a look at this graph.
5:28It very starkly illustrates these two
5:31different potential futures.
5:34The little wiggly black line on the left-hand side is the
5:37temperature that we've had so far.
5:40The big blue band is the temperatures that we could
5:43have under a scenario where we limit our greenhouse gas
5:47emissions very sharply.
5:50The big red band is the business as usual scenario.
5:55And as you can see, it gives us a rather frightening
5:58picture of temperatures in the future.
6:01If this business as usual scenario is sustained, for
6:05example, it's been predicted that the Greenland ice sheet
6:09could melt completely, leading eventually to sea level rises
6:14of more than seven metres.
6:16To put this really into perspective, 1 and 1/2 degrees
6:21increase would give us a warmer world than at any time
6:25that humans have been on the planet.
6:28If we got to 4 and 1/2 degrees, it would be the
6:32warmest planet than we've had for millions
6:34and millions of years.
6:37Well, that's the gloomy prospect.
6:39But the good news is that if we can start to reduce our
6:42greenhouse gas emissions straight away and pretty
6:46sharply, the temperatures in the second half of this
6:49century will be considerably less than those business as
6:52usual predictions.
6:54It's important to realise though at this stage, that
6:57there's a lot of momentum in the climate system.
7:01If we were to, by some miracle, stop emitting all
7:04greenhouse gases today and forever more, we would
7:08probably still get about a degree of warming by about
7:112030 because of all the greenhouse gases in the system
7:14that we've already put there.
7:16The moral of this story is, the sooner
7:18we start, the better.
7:21In the next few topics, I want to explore why we need to
7:25apply the brakes to our climate system as soon as we
7:28possibly can.