Future climate projections: Five graphs from three reports
- 28 Nov 2012, 15:00
- Robin Webster
Three different reports released in advance of the latest
instalment of the international
climate talks in Doha all carry more or less the same message.
On current trends the world is increasingly unlikely to avoid a
temperature rise of two degrees above pre-industrial levels - and a
four degree rise is possible, they say.
We've pulled out some of the most interesting statistics and
graphs to summarise the different reports.
The World Meteorological Organisation's greenhouse gas
bulletin
First, the World Meteorological Organisation (WMO) - a specialised
United Nations agency - released its
annual greenhouse gas bulletin. The findings are based on data
gathered by the WMO's Global
Atmosphere Watch Network, which monitors the amount of
greenhouse gases in the atmosphere.
The WMO's top-line conclusion is that greenhouse gas
concentrations in 2011 were the highest on record. Carbon dioxide,
methane and nitrous oxide - the greenhouse gases driving additional
warming - are now 140 per cent, 259 per cent and 120 per cent
higher than pre-industrial levels, respectively.
Given that global greenhouse gas emissions continue to
accumulate in the atmosphere, the 'record high' may not be that
surprising. But the WMO also concludes that despite international
commitments to cut greenhouse gas emissions, the amount of carbon
dioxide in the atmosphere has continued to increase at a fairly
steady rate over the last decade.
The report also looks briefly at the role of forests and oceans
as carbon sinks, which absorb some manmade emissions. The graph
below shows that as carbon emissions have increased (yearly change,
in green), the concentration of carbon dioxide in the atmosphere
has also increased (yearly change, in blue). But not as fast as it
might have done - because around half of carbon dioxide emissions
have been absorbed by the world's carbon sinks (yearly change, in
red):
Source: WMO Bulletin. The graph shows annual emissions of
carbon, annual increase in concentration of carbon, and the amount
of carbon sequestered by sinks each year. The figures are based on
research by
Ballantyne and colleagues, 2012 and
Levin, 2012.
In other words, the natural world has absorbed some of the rise
in manmade carbon emissions, although it may not continue to
perform this service for us in the long
term.
UNEP emissions gap report
The United Nations Environment Programme (UNEP)'s emissions
gap report is compiled on an annual basis. It aims to calculate
the 'gap' between emissions reductions promised by governments
around the world, and the emissions cuts needed to limit
temperature rise to two degrees Celsius.
There's a range of uncertainty in projecting future temperature
rise, but the gap is getting bigger, says UNEP. It's illustrated in
the following infographic, which also captures the range of
uncertainty in the two degrees projection - (in grey):
The grey descending patch shows the range of emissions
reductions from all greenhouse gases consistent with being on a
track for a two-degree temperature rise. (The fact that this is a
range, rather than a single pathway, reflects uncertainty.)
The four green lines show different projections of global
emissions pathways, based on promises made by countries at the
moment and the extent to which they are implemented. UNEP's
conclusion - reflected in the graphic - is that there is still a
substantial gap between political ambition and limiting temperature
rise to two degrees Celsius.
Future emissions by country
Less abstractly, the UNEP report also includes interesting
graphs of past, present and (possible) future emissions from
different parts of the world.
This graph shows emissions from a selection of G20 countries
since 1990, and information on what those countries have said their
emissions will be by 2020:
Source: Figure 2.6, UN Emissions gap report. The graph uses
national-level data.
China's projected emissions growth sticks out. To add detail,
the next chart changes the pattern considerably by comparing
emissions per capita, (per person) rather than overall emissions.
At current rates of growth, China's per capita emissions are going
to remain substantially below those of some other developed
countries - although according to this assessment they will reach
or surpass European levels.
Source: Figure 2.8, UN Emissions gap report. The graph uses
UN population
data.
World Bank - Four degrees
The
World Bank also released a report at the beginning of last
week, warning that if countries don't fulfil current emissions
reduction promises, the world could see four degrees celsius
temperature rise by the end
of this century.
Projecting future temperature rise is tricky, as it depends on
how sensitive the climate is to carbon emissions in the longer
term, and how man made emissions change over the century.
But even with such uncertainty in the system, the message of the
report is that the current level of ambition on emissions cuts in
not adequate to rule out higher levels of temperature rise.
The graph below illustrates temperature projections for a
selection of future emissions scenarios - and the one for current
pledges to cut emissions (in purple) exceeds the limit of emissions
which gives a fifty per cent chance of avoiding more than two
degrees celsius temperature rise.
Source: Figure 22, "
Turn down the heat", World Bank. The high emission scenarios
are created by the
IPCC. Data for the low-emission scenarios taken from
Hare and colleagues, 2011,
Rogelj and colleagues 2010 and
Schaeffer and colleagues 2012.
The "current pledges" scenario - the purple line - gives a 50/50
chance of a temperature rise above 3 degrees celsius, the report
says. But it also notes:
"Even with the current mitigation
commitments and pledges fully implemented, there is roughly a 20
percent likelihood of exceeding 4°C by 2100."
Three reports - roughly the same message
Despite promises from countries to cut their emissions, the
world's greenhouse gas emissions continue to rise, making higher
levels of temperature rise this century more likely.
That's the clear conclusion of these three reports, which also
suggest that the task of limiting temperature rise to 2 degrees or
less above pre-industrial levels is becoming increasingly
challenging. In contrast, future scenarios where the world
experiences a temperature rise of 4 degrees or higher are looking
increasingly plausible.