It is now becoming increasingly clear that humanity will probably not be able to limit global warming to 1.5 degrees above pre-industrial levels. For this reason, a research team has now used an ensemble of 35 climate models and statistical methods to take a closer look at how warming of two degrees will affect our world - and what this means for individual regions. The results confirm, among other things, that humidity, rain and heat will also increase in our latitudes, while the winds are weakening at the same time. In the Amazon region and many parts of the higher latitudes, however, it is becoming windier, drier and the risk of forest fires is increasing.
In the Paris Climate Agreement, the international community of states agreed to limit global warming to 1.5 degrees compared to pre-industrial conditions if possible, but in any case to two degrees. In the meantime, however, it has been almost seven years since the agreement and hardly anything has happened. Greenhouse gas emissions are still increasing at an almost unchecked rate and, according to studies, there is little chance of meeting the 1.5 degree target. Instead, warming is already at 1.14 degrees and climate researchers predict that the 1.5 degree limit will be exceeded in the next few years. At the same time, the Intergovernmental Panel on Climate Change (IPCC) warned in 2018 of the far-reaching consequences of a two-degree warming. Even half a degree more than the 1.5 degree target could significantly increase weather extremes, water shortages and the loss of ecosystems.
exceeding the two-degree mark in the 2040s
But what does this mean specifically? "Understanding the climate changes occurring at two degrees and their spatial heterogeneity is important so that decision-makers can prepare appropriate adaptations and action plans," explain Taejin Park of NASA's Ames Research Center and his colleagues. Only then can one identify where and to what extent lives and livelihoods are endangered. To refine the forecasts accordingly, Park and his team used an ensemble of 35 climate models from the Coupled Model Intercomparison Project (CMIP). In addition, they used special statistical methods to increase the spatial resolution of these model forecasts from around 200 by 200 kilometers to 25 by 25 kilometers. Their forecast model, created with the help of supercomputers, also has a high temporal resolution that goes beyond monthly averages and can also reflect daily fluctuations. This is particularly important to capture extreme heat days or heavy rainfall.
On the basis of this new forecast model, the research team then first examined how the global climate will develop up to 2100 with moderate and unchecked climate change and when the two-degree limit will be exceeded. The result: In both scenarios, this threshold is expected to be reached in the 2040s, in the first case in 2041, in the second in 2044. “By then, global air temperatures over land will have risen by 2.33 and 2.79 degrees, respectively.” , Park and his team report. The reason for these higher land temperatures is that the oceans react more slowly to climate change and therefore act as cooler buffers. The forecast also confirms that some regions – as can already be observed – will warm up faster than the rest of the world. This includes the polar regions in particular. "According to the forecasts, Greenland, Alaska and northern Asia in particular will already have reached an increase in mean annual temperatures of more than three degrees by the 2040s," the researchers report. In southern Asia, Africa and southern South America, on the other hand, the warming will be weaker.
More heat stress, increased danger for the Amazon rainforest
In order to determine what specific consequences warming will have for different regions around the world, Park and his colleagues then examined the regional changes in six important climate parameters: precipitation, humidity, long- and short-wave solar radiation, wind speed and the so-called cool limit or wet bulb temperature. Temperature (Wet Bulb Temperature). This reflects how the combination of humidity and temperature affects the human body and where the limit lies that can still be tolerated without health consequences. The analyzes showed that the mean wet-bulb temperature will increase by around two degrees over most land areas in the 2040s. As a result, there will also be more days of extreme heat stress. "This is particularly true for western North America with 27 additional heat stress days, East Africa with 32 more days and the Sahel zone with 44 additional heat stress days," the scientists report. In Australia and South America, on the other hand, heat stress could decrease slightly.
At the same time, short- and long-wave solar radiation is increasing in most areas. Accordingly, there will be particularly high increases in the shortwave share in the Mediterranean region, in northern Europe and in eastern North America. On the other hand, the researchers predict above-average increases in long-wave thermal radiation for the Arctic and large parts of Africa. Precipitation will also increase in most areas. Park and his team have determined that the global average in the 2040s will be 13 to 20 millimeters more rain per year, depending on the scenario. However, there are major regional differences: In West and East Africa, 82 and 52 millimeters more rain falls per year, and in Southeast Asia, the amount of precipitation increases by 64 millimeters per year - a high proportion of this precipitation could fall as heavy rain. In contrast, there is less rain in many regions that are already dry, such as the southwest of North America, the Mediterranean region and Australia. The decline in precipitation in the Amazon basin is particularly drastic: Annual precipitation there will fall by 98 millimeters per year in the 2040s. At the same time, the relative humidity is falling there and the wind speeds are increasing.
This does not bode well for the Amazon rainforest: "The Amazon will experience more severe droughts, higher risk of fire and dangerous heat stress as the earth continues to warm," the scientists report. At least for some areas of tropical South America and Southeast Asia, the analysis also shows that the common assumption "dry areas are getting drier, wet areas are getting wetter" does not apply to them. Instead, it is also becoming significantly drier in these rainforest areas. "It is evident that the extent and direction of climate change differs by region, so the impacts are also very different," state Park and his colleagues. At the same time, the study confirms that progressive warming will further intensify many of the climate risks and impacts that already exist.
Source: Taejin Park (NASA Ames Research Center, Moffett Field) et al., Earth's Future, doi: 10.1029/2022EF003330