Sustainability

The climate is warming faster than it has in the last 2,000 years

In contrast to pre-industrial climate fluctuations, current, anthropogenic climate change is occurring across the whole world at the same time. In addition, the speed of global warming is higher than it has been in at least 2,000 years. That’s according to two studies from the University of Bern.

Many people have a clear picture of the "Little Ice Age" (from around 1300 to 1850). It’s characterized by paintings showing people skating on Dutch canals and glaciers advancing far into the alpine valleys. The fact that it was extraordinarily cool in Europe for several centuries is documented not only by historical paintings, but also by a large number of temperature reconstructions, for example using tree rings. As there are also similar reconstructions for North America, it was assumed that the "Little Ice Age" and the similarly famous "Medieval Warm Period" (approx. 700 – 1400) were global phenomena. But now a group led by Raphael Neukom of the Oeschger Centre for Climate Change Research at the University of Bern is painting a very different picture of these alleged global climate fluctuations. In a study in the well-known scientific journal "Nature" and in a supplementary publication in "Nature Geoscience", the team shows that there is no evidence that there were uniform warm and cold periods across the globe over the last 2,000 years.

Climate fluctuations in the past varied from region to region

The authors of the study see the explanation for that as being that regional climates in pre-industrial times were primarily influenced by random fluctuations within the climate systems. External factors such as volcanic eruptions or solar activity, for example, were not intense enough to cause markedly warm or cold temperatures across the whole world simultaneously for decades, or even centuries.

Not only absolute temperature values were calculated, but also the probability of extremely hot or cold decades and centuries. The result: No globally coherent picture emerged during the periods being investigated. "The minimum and maximum temperatures were different in different areas," says Raphael Neukom. So thermal extremes across the world cannot be inferred from regional temperature phenomena like the oft-mentioned "Medieval Warm Period" in Europe and North America.

The current warm period is happening across the world for the first time

However, global trends can be demonstrated for the recent past. Both studies show that the warmest period of the last 2,000 years was most likely in the twentieth century. On more than 98 percent of the Earth's surface. This shows – once again – that modern climate change cannot be explained by random fluctuations, but by anthropogenic emissions of CO2 and other greenhouse gases. What we didn’t know until now is that not only average global temperatures in the twentieth century are higher than ever before in at least 2,000 years, but also that a warming period is now affecting the whole planet at the same time for the first time. And the speed of global warming has never been as high as it is today.