‘Unequivocal’ global warming

The 2013 IPCC report

Simon Oakes

‘Unequivocal’ global warming

What this presentation covers

1 What is the IPCC?

2 What are the key findings of the 2013 IPCC report?

3 What is happening to sea level?

4 Why is there still uncertainty about the severity of future change?

5 What can be done about climate change?

‘Unequivocal’ global warming

The data show a warming world

Insert graphic see his orig

In the last 100 years there is

a strong upwards

movement away from the

established trend

Earlier data show some

natural variability, but suggest a fairly

steady long-term trend

‘Unequivocal’ global warming

How does warming vary

• Look at the world map on pages 20–21 of Geography Review

• Watch the NASA video of changing global temperature anomalies, 1880–2012 at:

http://www.nasa.gov/topics/earth/features/2012-temps.html

• How does warming vary with:

(a) latitude?

(b) continentality?

‘Unequivocal’ global warming

How far will temperatures rise?

• The latest report states that it

is‘likely’ we will see a global

temperature rise of at least 1.5ºC by

2100, assuming a doubling of GHG.

• Temperature could rise by as much

as 4.8ºC or as little as 0.3ºC

according to different projections.

• As exam practice, compare the two

projected trends shown in the

diagram.

‘Unequivocal’ global warming

Evidence of a warmer world

• Major ice sheets have lost

mass.

• Land-based glaciers

continue to shrink.

• Arctic sea-ice cover has

fallen since 1979.

• The IPCC is ‘virtually

certain’ of further

permafrost melting

‘Unequivocal’ global warming

Sea-level riseSea level is rising. The world has recorded a

20 cm rise since 1900. A warming climate

affects the oceans in two ways to bring this

eustatic rise:

1Thermal expansion – as water warms it

expands, like liquid in a thermometer.

2Large amounts of water are locked on land

in glaciers and permafrost. When this

melts water pours into oceans.

Local isostatic changes – such as land

subsidence in delta regions – increase sea-

level rise further in some places.

‘Unequivocal’ global warming

Summary of sea-level rise

•The equation looks simple: so why is there such uncertainty over just how

much sea-level rise will actually take place (the latest IPCC estimates range

from 26 to 82 cm)?

•The answer lies with the complexity of positive feedback effects

taking place in the Earth–atmosphere system (see next slide).

‘Unequivocal’ global warming

Climate-change uncertainty

•Loss of snow and ice

cover in the Arctic means

less sunlight is reflected.

Warming accelerates.

•The release of

methane, a potent

greenhouse gas, from the

melting of the Arctic

tundra increases GHG in

the atmosphere,

triggering a second

feedback loop.

‘Unequivocal’ global warming

Climate change uncertaintyThere are other causes of uncertainty for climate-change modelling and extreme

weather event attribution.

El Niño and La Niña events naturally last for a few years and

cause weather changes

The North Atlantic Oscillation is another climate phenomenon that may be linked with the recent extreme weather in the UK

Scientists do not fully understand the role that oceans play in absorbing warming

Sunspot activity brings change in average

temperatures, although not a sustained rise

‘Unequivocal’ global warming

What can be done?