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Checking the Facts: Is Global Warming Just a Natural Cycle? | Environment | All topics from climate change to conservation | DW


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It is true that in its 4.5 billion years of history, planet Earth has experienced periods of lesser and greater heat.

Altering over thousands of years, these temperature changes have been determined by variations in the Earth’s orbit around the sun. While greater distances resulted in colder cycles, movements closer to the heatball led to warmer interglacial periods.

At the end of the 20th century, when scientists began to examine the evolution of temperatures over time, they observed a much faster rate of global warming from the 1980s onwards than had previously been recorded.

In 1998, researchers at the American University of Massachusetts Amherst and the Tree Rings Research Laboratory at the University of Arizona published a study showing the average annual global temperature over the past 1000 years.

To calculate past temperatures going back half a millennium before the thermometer was invented, they looked at what are called indirect or natural records – measurements of ice cores, tree rings and corals.

The result showed little variation for several hundred years until the 20th century, when there was suddenly a big increase.

In 2013, research published in the journal Science analyzed even older temperatures, dating back 11,000 years. The conclusion was the same: Our planet has warmed faster over the past century than at any time since the end of the last Ice Age.

The study also found that over the past 2,000 years, the Earth was actually in a period of natural cooling in terms of its position relative to the sun.

But this natural cooling has not been recorded due to unprecedented warming caused by human greenhouse gas emissions, the newspaper explains.

What is the link between CO2 emissions and climate change?

The greenhouse effect – a natural process that warms the Earth – is necessary to sustain life on the planet. It happens when certain gases in our atmosphere trap heat emitted by the Earth and act as the planet’s own greenhouse. Natural heat trapping gas in our atmosphere, which include carbon dioxide (CO2), methane, and nitrous oxide, are needed to keep the Earth’s surface temperature warm.

Without greenhouse effect, surface temperatures would drop 33 degrees Celsius (59.4 degrees Fahrenheit), according to the World Meteorological Organization (WMO) – making the planet a frozen and uninhabitable place.

For thousands of years, nature had well regulated the concentration of these gases. But that started to change when humans began to burn fossil fuels as a global means of creating energy, resulting in a surge in unnatural CO2 emissions. It interfered with the energy balance of the planet.

And, as a result, the Earth began to heat up faster.

According to the WMO State of the World Climate 2020 report, the average temperature last year was 1.2 degrees Celsius (2.2 Fahrenheit) higher than pre-industrial levels. This refers to the period between 1850 and 1900, when fossil fuels were not widely used as a means of producing energy.

The report describes the increasing levels of greenhouse gases in the atmosphere resulting from human activities, such as “A major factor in climate change”.

Infografik CO2-Budget der Erde FR

In 2001, the Intergovernmental Panel on Climate Change (IPCC) estimated that the concentration of CO2 in the atmosphere had been 280 parts per million (ppm) several thousand years before the industrial age. In 1999, it had risen to 367 ppm, according to the IPCC.

Established as a United Nations body in 1988, the IPCC has 195 member countries and assesses science related to climate change. He attributed the increase in atmospheric CO2 to anthropogenic (human-made) emissions, three-quarters of which from fossil fuel combustion and the rest from land use change.

In May 2021, the global average level of atmospheric CO2 reached 415 ppm . The last time CO2 levels were so high was around 3 million years ago, when sea level was about 30 meters (100 feet) higher and modern humans n ‘did not even exist.

Benjamin Cook, a climatologist at NASA’s Goddard Institute for Space Studies, said that in the late 20th century, when researchers began looking for answers to explain the warming trend, they looked at different factors including greenhouse gases, solar energy, ocean circulation and volcanic activity.

“Only greenhouse gas emissions from fossil fuels and industrialization have given us a prediction that matches the warming we are seeing,” Cook told DW.

He said the scientific community today is as confident in human-caused climate change as it is in understanding the theory of gravity.

“There are uncertainties and nuances to be discussed in climatology,” Cook said. “But the one thing just about all scientists agree on today is that the warming we are seeing is caused by the burning of fossil fuels.”

Why did it take a long time to come to this conclusion?

A widely debated subject Analysis of the evolution of the scientific consensus on anthropogenic global warming was published in 2013.

Led by John Cook, a researcher at the Climate Change Communication Research Center at Monash University in Australia, researchers from the US, UK and Canada reviewed 11,944 climate summaries published in the peer-reviewed scientific literature between 1991 and 2011.

Less than 1% of the research articles they reviewed rejected the idea of ​​human influence on our climate. And while 66.4% of the summaries expressed no position on the anthropogenic factor, 32.6% agreed. Further analysis of the latter figure revealed a 97.1% consensus on man-made climate change.

Critics, however, criticized the results on the grounds that the 97.1% consensus came from less than a third of all articles reviewed. Most, they said, had not expressed an opinion.

Scientific consensus, however, cannot be achieved by voting, but evolves over time as more and more research is done.

Factory, emissions, industry

Energy production based on the combustion of fossil fuels is the largest source of CO2 emissions

A more recent study conducted by a group of international authors confirmed that more than 90% of climatologists share the consensus that climate change is caused by humans.

And a 2019 Analysis of 11,602 peer-reviewed papers on climate change published in the first seven months of 2019 found scientists had reached 100% agreement on anthropogenic global warming. This research was conducted by James Lawrence Powell, an American geologist and author of 13 books on climate change and earth sciences.

“If an alternative theory of what causes climate change rather than greenhouse gases were supported by research and evidence, such work would be groundbreaking,” said Benjamin Cook. “It would be a Nobel Prize-level study. But we don’t see this research.”

Man-made climate change is endorsed by the IPCC. As early as 1995, the intergovernmental body declared“The balance of evidence suggests a discernible human influence on the global climate. “

“A scientific approach is to look at data, observations and model results to draw conclusions,” said Helene Jacot Des Combes, climatologist at the University of the South Pacific, author of the IPCC and adaptation advisor to the Government of the United States. Marshall Islands.

“And all of this tells us that the current climate change is caused by human activities.”

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