Some scientists say the blizzard is an example of human-caused climate change because it was an extreme weather event. The increases in heavy precipitation have led to runoff and caused major flooding events throughout the Northeast, as well as the Midwest and Great Plains. Such increases in rain activity are unlikely to occur naturally and may be due in part to human-induced climate change.
Severe to exceptional drought conditions proliferated in the American Southwest at the beginning of spring. Fish in the Rio Grande had to be relocated, and farmers along the Middle Rio Grande in New Mexico were told to expect half their irrigation allotment. The drought contributed to an abnormally intense fire season in northwestern Colorado and led to the first-ever rationing of water usage along the Yampa River Valley in the basin's history, as well as other serious impacts on people, agriculture, and wildlife in the area.
In February of , record-setting levels of rain in California led to floods throughout the northern part of the state. Scientists predict that extreme precipitation events will continue to increase in intensity in California in the future, as well as greater variability between wet and dry years — meaning more droughts and more floods. Snowpack in the western states was dramatically lower in the winter of According to the National Climate Assessment, the reduced snow levels are part of a larger trend of declining winter snowpack throughout the southwestern United States over the last 50 years, due largely to warmer temperatures that cause precipitation to fall as rain rather than snow and cause the existing snowpack to melt earlier in the year.
Snow drought can lead to reduced water availability in the summer and have negative impacts on economies that rely on outdoor tourism and recreation. Snow drought can also have other impacts on people, agriculture, and wildlife. For the first time in over seven years, California was officially declared free of drought in March The drought led to major losses in the California agricultural sector, significant environmental damage, and water shortages in some rural areas.
Many scientists have concluded that human-induced climate change has substantially increased the likelihood of extreme droughts in California, and contributed to the state's most recent drought emergency. After historic amounts of rain fell in the winter of and the snowpack level rose, much of the western United States experienced an early spring melt, leading to increased risk of flooding and dangerous fluctuations in river flow.
The faster snowmelt is partially the result of warmer temperatures earlier in the year, causing spring conditions to arrive as much as 20 days earlier than normal in some parts of the country. Scientists say because of human-caused climate change, spring is beginning about 2. According to the Third U. National Climate Assessment, heatwaves in the United States have become more frequent since the s, while the frequency of cold waves has declined. This evolution also affects very rare events: for example, a hot event that occurs on average every 20 years in the current climate — referred to as a return period of 20 years — would occur on average every other year by in RCP8.
In the same scenario, its cold equivalent has its return period increasing from 20 years to more than a century. Despite these trends, the occurrence of extreme cold is still possible. Even in a strong scenario, it is to be expected that some cold records will be broken locally in the 21st century , but much less frequently than warm records.
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For example, in the United States, the ratio between the occurrence of hot records and the occurrence of cold records is currently it is estimated at around and in in the moderate scenario. In addition to the uncertainties associated with the scenario selection and with the internal climate variability , the future evolution of temperature extremes is sensitive to the choice of the numerical climate model , particularly at regional and seasonal scales.
In Europe, in the RCP8. These uncertainties also affect the characteristics of multi-day events. For example, although future projections agree on the increase in the frequency, intensity and duration of European summer heatwaves, their evolution by varies by a factor of three, for a given scenario, depending on the numerical model considered.
Figure 5. Schematic representation of a change in the summer temperature distribution in France with, in addition to a simple translation warming, from black to red curves, see Fig.
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In this latter case, the probability of hot extremes further increases. Same legend as Figure 2. In Europe, future projections suggest a small increase in variability in summer, making warm extremes even more likely, and a small reduction in winter, making cold extremes even less likely. These behaviours are respectively linked to a drying of the soil in summer and a decrease in snow cover in winter. Figure 6. The averages are indicated by thicker lines. The anomaly observed in 2. Early August would remain warm at the end of the century, even in this strongest scenario.
However, in the RCP2. Moreover, locally in France and on a scale of a few days, the hottest days of August remain unusually hot even in in the RCP8. The answer therefore depends on the scenario and on the spatial and temporal scale considered. Apart from the temperature increase, the increase in the greenhouse effect is likely to disrupt the global hydrological cycle water exchanges between the atmosphere, the ocean and continents; read: Are we at risk of water shortage? The response of hydrological extremes is particularly difficult to understand because of its spatio-temporal heterogeneity and of the direct influence apart from climate change of humans on continental water flows and storage.
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For France, no systematic assessment of extreme precipitation trends is yet available. Figure 7. They are the subject of particular attention and some studies suggest a recent intensification of these events. However, it is more difficult to translate these changes into floods, as they are highly subject to increasing anthropogenic impacts e. Figure 8. Percentage of the French metropolitan territory affected by agricultural drought each year. The criterion used here is the first decile of soil moisture over the period , based on re-analysis data. To characterize them, indicators are used.
Meteorological droughts are the easiest to describe and show disparate trends from one region to another, sometimes largely influenced by natural climate variability in Sahel or more recently in California for example. Recent trends in agricultural droughts are more difficult to assess in the absence of a global network of in situ measurements and despite progress in spatial observation. An alternative is to simulate the evolution of soil water content in response to observed variability in meteorological parameters.
If this pithy motto is still the subject of debate within the scientific community, the drying up of the Mediterranean basin and more generally a poleward expansion of arid and semi-arid zones seems inevitable. As a result, the contrast between the European North wettest and South driest is expected to increase, and some recent work even suggests that most numerical climate models underestimate the summer drying of the northern hemisphere mid-latitudes.
Weather Extremes and Climate Change
These models also indicate a relatively widespread intensification of heavy precipitation events in response to global warming, including in areas that will experience an average drying. The exceptions to this increase in extreme rainfall are mainly in subtropical regions. In the simulations, this intensification of heavy rainfall is all the more pronounced as the scenario of increasing greenhouse gas concentrations is high.
Also, the shorter the period of analysis of precipitation accumulation daily to hourly accumulations , the more frequent and intense heavy precipitation is projected to be. However, these numerical results should be considered with caution due to the limited horizontal resolution of most models and their simplified representation of the processes associated with these extreme events.
The expected intensification of the hydrological cycle in warmer climates also results in an increased risk of drought in many parts of the world, including some regions where the average annual precipitation increases during the 21st century. This is due both to an increase in the temporal variability of precipitation increase in the number of consecutive days without rain and to an increase in evapotranspiration evaporation of continental surfaces and transpiration from plants to the atmosphere.
In summary, global warming therefore affects both ends of the precipitation distribution, making both intense rainfall events and drought episodes more likely. Mediterranean-type climates around the Mediterranean, but also some regions of Australia, South Africa, or America are likely to be particularly affected by these hydrological changes, while more generally, a shift of arid zones towards mid-latitudes is expected. In France, a decrease in the quantity of water available in the soil is expected, as well as a decrease in the low levels of most rivers.
Tropical cyclones, also known as hurricanes in the Atlantic or typhoons in the Pacific , are by far the most devastating meteorological events , both in terms of their power and of the population affected read Tropical Cyclones: development and organization and Tropical Cyclones: impacts and risks. It was only since the s that a systematic observation of cyclones has been possible with the advent of satellites. Thus, any trend estimated over the entire 20th century is questionable Figure 9.
Figure 9. Annual number of tropical cyclones or hurricanes in the Atlantic categories 1 to 5 on the Saffir-Simpson scale , and of the strongest hurricanes categories 3 to 5 on the same scale. This mode of variability corresponds to an oscillation of sea surface temperature anomalies in the North Atlantic on a time scale of several decades. The decades that followed were marked by greater hurricane activity in the Atlantic Ocean, which is difficult to compare with the previous positive phase of the AMO due to the lack of quality data, particularly satellite data. Climate breakdown will create volatile social situations.
Large numbers of people could be forced to move within their countries and across borders — both near and far. Extreme environmental events and rapid change could also destabilise economies , leading to unemployment, pressure on resources, spiralling living costs and political and social unrest. Societies faced with economic insecurity, real or perceived competition for resources, pressured public services and rapid social and cultural change can quickly grow disaffected if faced with unresponsive politicians and no hope of change.
Our investigations have found that these groups are already exploiting the issue — with climate denial and climate conspiracies finding a welcome home in the ideology of both the populist right and the far right. The war-driven migrant crisis in showed how quickly and powerfully anti-immigrant feeling can distort and destabilise politics as we know it, surging far beyond any initial racial, religious and cultural friction.