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Why we’ll overshoot the 1.5°C goal

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“Overshooting any temperature goal would generate risks of triggering feedback accelerations, such as the enhanced release of carbon from the thawing of soils that are currently frozen, or causing large-scale and potentially dangerous impacts that could be difficult to reverse, such as a loss of species, inundation of some land areas, or extensive bleaching of corals. More research is needed into the likelihood of triggering feedbacks or irreversible impacts, such as large rises in sea level, during temporary overshooting of a 1.5°C goal.”

So says a new report, ‘Mitigating climate change through reductions in greenhouse gas emissions: is it possible to limit global warming to no more than 1.5°C?’, which aims to inform negotiations at the United Nations climate change conference, taking place in Bonn, Germany, between 2 and 6 August 2010.

Global average temperature has already risen by about 0.8°C since the end of the 19th century. The report concludes: “Even if global emissions fall from 47 billion tonnes of carbon-dioxide-equivalent in 2010 to 40 billion tonnes in 2020, and are then reduced to zero immediately afterwards, we estimate that there would be a maximum probability of less than 50 per cent of avoiding global warming of more than 1.5°C above the pre-industrial level”.

The report is jointly published by the Grantham Research Institute on Climate Change and the Environment, the Centre for Climate Change Economics and Policy, and the Met Office Hadley Centre.

Scientific evidence that our world is warming was released in the ‘2009 State of the Climate’ report, issued by the US National Oceanic and Atmospheric Administration (NOAA). The report draws on data from 10 key climate indicators that all point to that same finding — the world is warming.

The 10 indicators of temperature have been compiled by the Met Office Hadley Centre, drawing on the work of more than 100 scientists from more than 20 institutions. They provide, in a one place, a snapshot of our world and spell out a single conclusion that the climate is unequivocally warming. Relying on data from multiple sources, each indicator proved consistent with a warming world.

Seven indicators are rising and three are declining.
Rising indicators
1. Air temperature over land
2. Sea-surface temperature
3. Marine air temperature
4. Sea-level
5. Ocean heat
6. Humidity
7. Tropospheric temperature in the ‘active-weather’ layer of the atmosphere closest to the Earth’s surface

Declining indicators
1. Arctic sea-ice
2. Glaciers
3. Spring snow cover in the northern hemisphere

Dr Peter Stott, Met Office Head of Climate Monitoring and Attribution and contributor to the report says: “Despite the variability caused by short-term changes, the analysis conducted for this report illustrates why we are so confident the world is warming.”

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