‘Unequivocal’ global warming The 2013 IPCC report Simon Oakes

‘Unequivocal’ global warming What this presentation covers 1What is the IPCC? 2What are the key findings of the 2013 IPCC report? 3What is happening to sea level? 4Why is there still uncertainty about the severity of future change? 5What 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: 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 The IPCC is ‘virtually certain’ of further permafrost melting

‘Unequivocal’ global warming Sea-level rise Sea level is rising. The world has recorded a 20 cm rise since 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 Thermal expansion Melting land ice Eustatic 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 Arctic albedo change Permafrost melting Positive feedback and accelerated global warming 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 uncertainty There 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? Adaptation This means dealing with the impacts of climate change, for instance by strengthening flood defences The long-term costs of adaptation to a much warmer world may be greater than spending money on mitigation in the short-term Mitigation This means slowing global warming by tackling the underlying problem of the build-up of GHG, for instance, by switching to renewable energy sources The global economic slowdown has hampered mitigation efforts Carbon intensity This is a measure of how much carbon dioxide is produced in relation to GDP A country like China whose GDP is rising can partially mitigate by decreasing the carbon intensity of its GDP as that figure rises But total emissions will still rise