00:02humans dependence on fossil fuels is
00:06heating up the planet with an
00:07unprecedented rate governments and
00:10policymakers must take urgent action
00:14that action is guided by what science
00:17says by the impact of climate change on
00:19the earth this is how it's calculated
00:32this is ver Hamby Agnes at the end of
00:35the 19th century he devised formulas
00:38which linked the flow of heat water and
00:40air 50 years later his ideas were the
00:43basis of the first computer model the
00:46atmosphere a modern day weather
00:48forecasting is born today's climate
00:51models are the highly evolved
00:52descendants of that original except the
00:55computers as some twenty-five trillion
00:57times faster here's how it works
01:00scientists divide the Earth's atmosphere
01:02into a grid of hundreds of thousands of
01:05cells and stacks like a skyscraper the
01:08model used by the Met Office Britain's
01:11National Weather Service for example
01:13uses stacks which are 85 cells high the
01:17models then calculate how energy air and
01:20water vapor flow through each cell over
01:22a given time period well weather
01:25forecasting takes a snapshot of the
01:27atmosphere at a given time
01:29and predicts what will happen over the
01:30next few days climate models consider
01:33the atmospheres behavior over years and
01:35years simulating either the world as it
01:39or the world as it might be they sketch
01:42out the sort of processes and the sort
01:45of results that you might see and that
01:48allows you to inform policy to some
01:51extent one of the classic things that
01:53climate models have always done is just
01:55look at the world if the carbon dioxide
01:57level were twice as high as it is today
02:00that was one of the first ways that
02:02climate models began to illustrate the
02:05fact that greenhouse warming really was
02:07likely to be a problem in the 21st
02:08century for all their complexity these
02:12models have limitations although you're
02:16cutting the atmosphere into millions of
02:18cells the atmosphere it's a very big
02:20thing and a millionth of a big thing is
02:22still a pretty big thing so the cells
02:24tend to be there maybe hundreds of
02:26kilometers on a side
02:29this means the models often struggle to
02:31capture details like cloud cover and
02:34clouds play a key role in climate as
02:38greenhouse gases made the atmosphere
02:40warmer it changed the amount of water
02:42vapor it can hold and how air rises and
02:45falls that in turn changes the amount
02:48and character of cloud cover
02:51depending on where clouds form they can
02:54either trap sunlight which warms the
02:56planet will reflect it back into space
02:58cooling it and some processes which
03:02govern cloud formation work on a very
03:04small scale so you can't actually model
03:09those precise processes in the computer
03:12models they have to build various
03:13different rules of thumb mean for what
03:15would you expect the clouds to be doing
03:17how you do that means that your model
03:20will behave differently compared to
03:22someone else's model where they do that
03:26dozens of these models exist run by
03:29teams all over the world the modelers
03:33all want to capture the earth as close
03:35as possible to how it is but there are
03:37assumptions about how that actually
03:39works differ from model to model and the
03:41ways that they implement those
03:45some models tend to people say run hot
03:49so they tend to provide more warming for
03:51a given amount of carbon dioxide and
03:53some models tend to run a little cold
03:57every few years the models are brought
03:59together fed standardized questions and
04:02then their results are compared this
04:04helps scientists understand the
04:06strengths and weaknesses of different
04:08climate models and improves them of
04:13course it's impossible to assess the
04:15model's future projections but what
04:18researchers can do is compare the
04:20success of models from previous decades
04:22a recent report compared the models from
04:26the 1970s to the 2000s and it found that
04:31by and large they were reasonably good
04:34that the warming that would actually
04:35seen sat within the error bars for most
04:37of them so it gave us a like general
04:40sense that these things weren't
04:41completely out of the park the climate
04:46models are getting increasingly
04:47complicated capturing more aspects of
04:50the earth but there is one element that
04:52is impossible to model and it is the
04:55biggest contributor to climate change
04:59the thing about human activity is that
05:01you can't get it inside the model the
05:04model deals with sort of like physical
05:05laws of chemistry and physics and
05:08biology so that there's no way the model
05:10can say well in 2050 America will have
05:13stopped emitting carbon dioxide instead
05:16scientists take simplified results from
05:18these climate models and run them
05:20through economic models in 2013
05:24scientists use these models to examine
05:27the effect of different climate policies
05:29on the future temperature of the planet
05:31the first looked at what would happen if
05:34there was continued large-scale use of
05:36coal the second if there was continued
05:39use of fossil fuels but some use of
05:42renewable energy the third if there was
05:45a much higher uptake of renewable energy
05:47and the fourth if there was a lot of use
05:50of carbon capture technology more land
05:54the striking thing about those
05:57comparisons and by other combatants will
05:59come out later is the only really tough
06:02climate policies get you the sort of
06:04trajectories which keep the temperature
06:06in the words of the Paris agreement well
06:08under two degrees above the
06:09pre-industrial what these models tell us
06:12is that the current level of emissions
06:14reduction is not remotely enough to have
06:19any assurance that you will stay under
06:21two degrees left even less all right
06:23close to 1.5 degrees
06:25climate models don't predict the future
06:28and they're not perfect there is a long
06:30way to go before they fully represent
06:32all of Earth's intricate processes but
06:35for now they are the only way the
06:37scientists have understanding how
06:39damaging an increase in carbon dioxide
06:41will be for the planet ultimately the
06:44solution to climate change won't lie
06:46inside models but rather what humans
06:49choose to do with the information they
06:51provide I'm Oliver Morton
06:54I'm the briefings editor at The
06:55Economist we've written a series of
06:57climate briefs to cover the basics and a
07:01bit more than the basics on all sorts of
07:03aspects of the climate crisis that's
07:05facing the earth you can read them all
07:06at the link opposite thank you for
