Rtl today – climate variability: twentieth century warming “unmatched” in 2000 years

Global temperatures rose faster at the end of the 20th century than at any time in the past 2,000 years, according to a study released Wednesday that experts say undermines questioning by climate deniers about the role of climate change. humanity in global warming.

As Europe suffocated in a second record-breaking heat wave in a month, the three peer-reviewed articles offered the most detailed snapshot of regional temperature trends dating back two millennia.

Climate variability – the fluctuation of surface temperatures over time – has long been the subject of debate.

While average global temperatures are currently about one degree Celsius (1.8 Fahrenheit) higher than in pre-industrial times, there have been a number of periods of cooling and warming over the centuries.

This has led skeptics of man-made global warming to suggest that human activity is not the primary driver of climate change.

The researchers used data compiled from nearly 700 temperature indicators, from tree rings, sediment cores, coral reefs, and modern thermometer readings, to provide a comprehensive timeline of recent climate history. our planet.

The results are clear: at no time in modern human history have temperatures risen as rapidly and steadily as at the end of the 20th century – the period when the post-war global economy , powered by fossil fuels, has reached unprecedented peaks in production and consumption.

The first article, published in the journal Nature, examined regional temperature trends over time.

Scientists have long known periods of unusual climatic activity, such as the Little Ice Age, a secular time when northern Europe experienced colder winters on average than at the start of the 20th century.

The study found that temperatures during the Little Ice Age and other abnormal periods did not rise or fall according to the global lockdown as had long been assumed, and varied regionally over much of the period. Last 2,000 years.

“When we go back in time, these are really regional phenomena, but they are not global,” said Nathan Steiger, of the Lamont-Doherty Earth Observatory at Columbia University.

This contrasts sharply with current warming trends.

“While in the contemporary warm period, it’s really global – 98% of the globe has this consistent warming after the industrial revolution – and that contrasts a lot with the climate variability that has occurred before over the past 2,000 years.”

– “Finally stop the climate deniers” –

A second article, in Nature Geoscience, examined rates of surface warming, averaged over sub-periods of a few decades each.

They found that pre-industrial temperature fluctuations were largely due to volcanic activity. But they also concluded that humans had never witnessed global warming so rapidly as in the latter part of the 20th century.

Author Raphael Neukom of the University of Bern, Switzerland, told AFP that the discovery “underscores the extraordinary nature of current climate change.”

A third study found that global temperatures leading up to the industrial era were cooled by a series of volcanic eruptions, which resulted in droughts in Africa and weak monsoons.

Commenting on the studies, Mark Maslin, professor of climatology at University College London, said their findings “should finally stop climate change deniers claiming that the recently observed consistent global warming is part of a natural climate cycle.”

“This article shows the truly striking difference between regional and localized climate change of the past and the truly global effect of anthropogenic (human-made) greenhouse emissions.”

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How does climate variability contribute to global crop failures?

According to a recent paper published on July 3 in the journal Scientists progress (1). For example, in 1983, ENSO was responsible for the largest synchronous harvest failure in recorded modern history.

Globally synchronous harvest failures refer to the simultaneous failure of a single harvest in several as far apart as the United States, China, and Argentina. And many researchers predict that these events will become much more frequent due to climate change. So how important is the risk of potential failures on a global scale for food security?

Current models of the global agricultural system assume that crop failures in geographically remote areas are unrelated. However, the new findings suggest that to make global food systems more robust, we need to learn more about the most damaging consequences of so-called multiple “breadbasket” failures. Especially since about two-thirds of the world’s staple foods are produced by about 25 percent of the planet’s cropland. And fewer people than ever have insufficient access to enough food, the authors write. In addition, an increasing number of people depend on imported food to meet their minimum daily caloric needs.

Researchers at Columbia University’s International Institute for Climate and Society Research, in collaboration with the International Food Policy Research Institute (IFPRI), assessed how different modes of climate variability cause volatility in global and regional agricultural yields. The study is the first to estimate the extent to which different modes of climate variability influence the volatility of global and regional agricultural production.

In particular, they examined the impact of ENSO, the Indian Ocean Dipole and other well-understood climate models on global production of maize, soybeans and wheat. More specifically, they analyzed how these modes of climate variability influenced drought and heat in the main growing regions.

Globally, maize is the most sensitive to climate variability, which accounts for about 18% of the year-to-year variation in maize production. While only 7% and 6% of the variation in soybean and wheat yields is linked to changes in global productivity, and therefore are less at risk of simultaneous failures.

The researchers also found that the risks are greater for poor farmers in developing countries who lack adequate coping mechanisms and lack the infrastructure and resources to handle large fluctuations in crop yields.

In addition, certain geographic regions, such as Africa and Brazil, are more exposed to the perils of climate variability. For example, ENSO and other recurring climatic phenomena account for 40 to 65% of the variation in food production in Africa and northeastern Brazil, the authors report. While other regions experience fluctuations closer to 10 percent.

Despite these large differences, the results reveal a definite link between climate models in several regions. Additionally, the authors suggest that these results can be extended to monitor and possibly even predict the influence on global production and potential global crop failures.

(1) Anderson, WB et al. Synchronous poor harvests and climate-driven variability in production. Scientific advances (2019). DOI: 10.1126 / sciadv.aaw1976

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