Floods, droughts, tropical hurricanes, tornadoes, wildfires, thunderstorms and lightning are all calamities related closely to processes on the earth’s surface; they are induced directly by the weather.
Extraordinary downpours such as those responsible for recent deadly flooding in the US, Western Europe, China and India are becoming more frequent, and more intense, as a result of climate change.
Global annually averaged surface air temperature has increased by about 1.8F (1C) over the last 115 years (1901–2016), indicates the US Global Change Research Program (USGCRP) in a climate assessment.
This period is now the warmest in the history of modern civilization. The last few years have also seen record-breaking, climate-related weather extremes, and the last three years have been the warmest years on record for the globe. These trends are expected to continue over climate timescales, USGCRP noted.
This assessment concludes, based on extensive evidence, that it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century.
In addition to warming, many other aspects of global climate are changing, primarily in response to human activities, USGCRP experts say. Thousands of studies conducted by researchers around the world have documented changes in surface, atmospheric, and oceanic temperatures; melting glaciers; diminishing snow cover; shrinking sea ice; rising sea levels; ocean acidification; and increasing atmospheric water vapour.
For example, USGCRP said, global average sea level has risen by about 7-8in since 1900, with almost half (about 3in) of that rise occurring since 1993. Human-caused climate change has made a substantial contribution to this rise since 1900, contributing to a rate of rise that is greater than during any preceding century in at least 2,800 years.
Global average sea levels are expected to continue to rise - by at least several inches in the next 15 years and by 1-4ft by 2100. A rise of as much as 8ft by 2100 cannot be ruled out.
Changes in the characteristics of extreme events are particularly important for human safety, infrastructure, agriculture, water quality and quantity, and natural ecosystems. Heavy rainfall is increasing in intensity and frequency across the United States and globally and is expected to continue to increase.
The magnitude of climate change beyond the next few decades will depend primarily on the amount of greenhouse gases, especially carbon dioxide, emitted globally. Without major reductions in emissions, the increase in annual average global temperature relative to preindustrial times could reach 9F (5C) or more by the end of this century. With significant reductions in emissions, the increase in annual average global temperature could be limited to 3.6F (2C) or less.
Continued growth in CO2 emissions over this century and beyond would lead to an atmospheric concentration not experienced in tens to hundreds of millions of years, USGCRP said.
There is a broad consensus that the further and the faster the earth’s systems are pushed towards warming, the greater the risk of unanticipated changes and impacts, some of which are potentially large and irreversible.
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