Turn down the heat: why a 4°C warmer world must be avoided

Turn down the heat: why a 4°C warmer world must be avoided

World Bank report on the likely consequences of a four degrees Celsius rise in global temperatures

This report, produced for the World Bank by the Potsdam Institute for Climate Impact Research and Climate Analytics, attempts to describe what climate change impacts are likely to be felt in a ‘4°C world', i.e. a world where global average temperatures have risen four degrees Celsius above pre-industrial levels. In doing so, it hopes to motivate actors and insert urgency into climate change mitigation and adaptation efforts.

The report first discusses presently observed climate changes and impacts, with extensive data and analysis provided across numerous areas. These include the following.

  • Rising greenhouse gas (GHG) emissions: from a pre-industrial concentration of around 278 parts per million (ppm), the levels of carbon dioxide, as of September 2012, have reached 391ppm (increasing at a rate of 1.9ppm per year).
  • Warming and rising sea levels: coral reefs are at particular risk and increased acidification is also an issue of concern.
  • Loss of ice: summer ice in the Arctic has halved in the last few decades.
  • Extreme weather and climate: increased severity and frequency of droughts and storms, and greater temperature extremes.
  • Welfare impacts: it is estimated that just a degree Celsius rise in temperature could reduce economic growth by around 1.3 per cent.

The paper then goes on to describe likely projections for the 21st century should a ‘4°C world’ become reality. Particular focus is placed on sea level rise, changes in extreme temperatures and sectoral impacts (agriculture, water, ecosystems/biodiversity and human health). These impacts are largely determined through an assumed linear growth. However, the final section of the paper warns of non-linear accelerating effects and impacts should certain 'tipping-points' be breached (either by introducing 'feedback' or else triggering 'cascades' of interlinked effects).

The concluding remarks stress the importance of cooperative, international actions to avoiding an unacceptable four degrees Celsius rise in global temperature. A ‘4°C world’ would disproportionately impact less developed countries which are least equipped to deal with climate change. As well as the direct impacts on food security and loss and damage, a ‘4°C world’ would likely greatly impact efforts to eradicate poverty.
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