The impact of human-caused global warming has blocked important winter rains, with severe impacts on agriculture and tourism. Spain and Portugal are suffering from their driest climates in at least 1,200 years, according to the study, with severe impacts on both food production and tourism.

Most of the rain on the Iberian Peninsula is in winter, as a humid low pressure system blows from the Atlantic Ocean. But a high-pressure system along the coast, the Azores High, can block the wet weather front. The researchers found that winters with high pressure in the Azores increased dramatically from one in 10 winters before 1850 to one in four since 1980. These extremes are also pushing wet weather north, making heavy rains more likely in northern England and Scandinavia.

Scientists say more frequent high pressures could be caused by the climate crisis caused by human carbon emissions. The number of very large high pressures in the Azores in the last 100 years is really unprecedented if you look at the previous 1000 years. The Iberian peninsula has been hit by an increasing number of heatwaves and droughts in recent years, with May being Spain’s warmest on record. The 2017 forest fires that killed dozens of people in the region came after the climate crisis increased heatwaves by a factor of 10, while the Tagus River, the region’s longest, was at risk of completely drying up, according to environmentalists.

The new study, published in the journal Nature Geoscience, analyzed weather data going back to 1850 and a computer model of the climate replicated to 850 AD. The study found that in 1850 and before humans began to emit large amounts of greenhouse gases, the Azores experienced an extreme high pressure on average every 10 years. But after 1980, the frequency rose to every 4 years. The extremely massive Azores high pressure reduced average monthly rainfall in winter by about a third, the data showed. Further data from chemical analysis of stalagmites in caves in Portugal revealed that the low rainfall was closely related to the large high pressure in the Azores.

Computer simulations of climate over the past millennium cover the period up to 2005. But other studies covering later years are consistent with new findings that the Azores high is expected to continue to widen, further increasing drought in the Iberian Peninsula until global carbon emissions are cut to net zero.