Warming patterns

Global warming does not mean the same amount of warming over the whole globe. There is a distinct spatial pattern to the long-term changes.

The first map below shows the total change in temperature since the early-industrial era, and the second map removes the global average warming to highlight regions of above and below average warming.

The largest warming is seen in the Arctic, and the land regions are clearly warming faster than the ocean. The striking blue area in the North Atlantic is a region of very little warming, and this is due to a decline in the strength of the Atlantic overturning circulation which brings warm water from the tropics to the northern latitudes.

All these features of the warming have been long predicted in climate model simulations, for example in IPCC AR4 and IPCC AR5.


Technical details: spatial pattern of warming uses approach described in Hawkins et al. (2020) using Berkeley Earth dataset, and the changes are relative to 1850-1900.

Arctic surprise

In 2007, IPCC AR4 produced this figure showing projections of changes in Arctic sea ice extent in the summer (July-September). The different colours represent a wide range of different scenarios for future emissions. Observations (1979-2020, added purple line) have decreased far more rapidly than projected in the CMIP3 models used at the time, when plotted on the same scale with the same reference period.

This demonstrates the concept of a climate-related ‘surprise’, or what might have been considered a low-likelihood event at the time.

The original figure is here. Also see Stroeve et al. (2012) for a CMIP5 comparison (Fig. 2a), and Notz et al. (2020) for a CMIP6 comparison (Fig. 2f).

What does a 1°C warmer world look like?

Global average temperature has risen by over 1°C since pre-industrial times, but the size of the change is not the same everywhere. The image below shows the temperature change observed in 5 individual years and for the 20-year average (2000-2019). For all of these examples the global average temperature was almost exactly +1°C warmer than the late 19th century.

In each individual year, the patterns can be quite different, with disparate regions of cooler and warmer temperatures. When averaging over 20-years, the overall pattern of warming is clearer: the Arctic is clearly warming much faster than the global average, and land areas are warming faster than ocean regions.


Continue reading What does a 1°C warmer world look like?

Sensitivity of historical climate simulations to uncertain aerosol forcing

Earth’s climate has warmed by approximately 0.85 degrees over the period from 1880 to 2012 [IPCC, 2013] due to anthropogenic emissions of greenhouse gases. However, the rate of warming throughout the twentieth and early twenty-first centuries has not been uniform, with periods of accelerated warming and cooling.

Guest post by Andrea Dittus
Continue reading Sensitivity of historical climate simulations to uncertain aerosol forcing

From the familiar to the unknown

Changes in climate are often analysed in terms of trends or differences over time. However, for many impacts requiring adaptation, it is the amplitude of the change (the ‘signal’) relative to the local amplitude of climate variability (the ‘noise’) which is more relevant.

We consider the ‘signal-to-noise’ ratio in observations of local temperature, highlighting that many regions are already experiencing a climate which would be ‘unknown’ by late 19th century standards. The emergence of observed temperature changes over both land and ocean is clearest in tropical regions, in contrast to the regions of largest change which are in the northern extra-tropics.

[Details in: Observed emergence of the climate change signal: from the familiar to the unknown, by Hawkins, Frame, Harrington, Joshi, Rojas & Sutton]
Continue reading From the familiar to the unknown

Glimpsing the future

In December 2019, the average temperature across Australia was about 2°C above what would be expected for the present-day, which is another 1.5°C above temperatures that were normal for December before humans started warming the climate. These extreme temperatures have contributed to the catastrophic bushfires which have devastated large areas.

But what may be considered ‘normal’ is constantly changing.

In a world which has warmed by 3°C – roughly the current global trajectory – what was extreme will be entirely normal.


Continue reading Glimpsing the future