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Projections of when temperature change will exceed 2 °C above pre-industrial levels


Climate change projections are usually presented as 'snapshots' of change at a particular time in the future. Instead, we consider the key question 'when will specific temperature thresholds be exceeded?' Framing the question as 'when might something happen (either permanently or temporarily)?' rather than 'what might happen?' demonstrates that lowering future emissions will delay the crossing of temperature thresholds and buy valuable time for planning adaptation. For example, in higher greenhouse-gas emission scenarios, a global average 2 °C warming threshold is likely to be crossed by 2060, whereas in a lower emissions scenario, the crossing of this threshold is delayed by up to several decades. On regional scales, however, the 2 °C threshold will probably be exceeded over large parts of Eurasia, North Africa and Canada by 2040 if emissions continue to increase — well within the lifetime of many people living now.

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Figure 1: Global mean surface air temperatures.
Figure 2: Proportion of GCM simulations that have a temperature above the 2 °C, 3 °C and 4 °C thresholds in each particular year.
Figure 3: Proportion of GCM simulations that have India's land-area mean surface air temperature above the 2 °C, 3 °C and 4 °C thresholds for different temperature metrics.
Figure 4: Spatial dependence of temperature increases and threshold-crossing times.
Figure 5: The likely earliest and latest times at which a 2 °C threshold is reached regionally for the IPCC SRES A1B emissions scenario.


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M.J., E.H. and R.S. are supported by the National Centre for Atmospheric Science (Climate). J.A.L. is supported by the Joint Department for Energy and Climate Change (DECC)/Defra Met Office Hadley Centre Climate Programme (GA01101) and by the DECC/Defra-funded Avoiding Dangerous Climate Change (GA0215) programme. The authors acknowledge M. Allen, A. Challinor and K. Shine for their input.

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Correspondence to Manoj Joshi.

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Joshi, M., Hawkins, E., Sutton, R. et al. Projections of when temperature change will exceed 2 °C above pre-industrial levels. Nature Clim Change 1, 407–412 (2011).

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