Last summer’s temperature rise could be worse than we thought

Since 2015, when the world’s governments promised to work to try to keep global temperatures from rising 1.5C above pre-industrial levels, it has always seemed likely they would fail to keep their word. Scientific data now shows that last summer in the northern hemisphere this target was already being exceeded by quite a margin.

In an area including the whole of Europe, most of North America and Asia the average temperature last summer was 2.07C hotter than between 1850 and 1900, the period that scientists have been using as the “reference period” to measure the averages before the industrial revolution began to alter the climate.

But it may be that even that measurement may be too optimistic. Scientists say that in the 19th century many of the thermometers and weather stations on which that average was based were not properly positioned or shielded from the sun, so it is possible that the world was cooler than the measurements reflect in Victorian times.

In order to get a better “average”, scientists used tree ring data from the whole of the northern hemisphere for the last 2,000 years and concluded that the temperate between 1850 and 1900 was 0.24C lower than had previously been estimated. In this case, last summer’s temperature rise would actually be 2.31C in these northern climes.