Climate can change abruptly due to natural or man-made forces
Key words: climate change, temperature, biosphere, glaciers, studies.
Results of a study on ice cores collected from tropical areas
For the first time, glaciologists compared elements found in ice cores taken from the Andes and the Himalayas to find out how the climate has changed, and is still changing, in tropical areas.
The National Science Foundation, Oceanic and Atmospheric Studies Administration and Ohio State University funded the research, said the university's press release on June 26.
The results of this work show a great cooling more than five thousand years ago and a more recent warming in the last fifty years.
They suggest that large glaciers in the tropics will disappear in the near future and indicate that in most countries of the world, glaciers and ice caps are retreating rapidly, even in regions with increasing precipitation. It follows that it is the rise in temperatures and not the decrease in precipitation that is the cause.
Researchers from the Polar Research Center at Ohio State University and three other universities put together time-series climate data recorded in seven remote locations north and south of the equator. Core samples taken from ice caps and glaciers have made it possible to trace the climatic history of each region, in some cases providing annual data and in others decadal averages.
“About 70% of the world's population now lives in tropical areas. So it's likely that when climate change occurs there, the effects will be significant, ”said geological science professor Lonnie Thompson, Ohio State University.
Over the past XNUMX years, Professor Thompson has organized some XNUMX expeditions to collect climatological data in glaciers and ice caps. The current study focuses on core samples taken from the Huascaran and Quelccaya ice caps in Peru, the Sajama ice cap in Bolivia, and the Dunde, Guliya, Puruogangri and Dasuopu ice caps in China.
The team of glaciologists extracted time series data from each ice core by calculating the ratio of two chemical forms of oxygen, called isotopes. This ratio is an indicator of the air temperature during the ice age.
All seven ice cores have provided clear data for each of the past four hundred years and decadal averages going back two thousand years. “We have data going back two thousand years and when you graph it you can see the medieval period of warming and the Little Ice Age,” he said.
During the medieval period of warming, which ranges from 1000 to 1400, the temperatures would have been a few degrees higher than those of the anterior and posterior periods. Its climatic effects were mainly felt in Europe and North America.
The next period, the Little Ice Age, from 1400 to 1800, saw an increase in glaciers in the mountains and a cooling of global temperatures, especially in the Alps, Scandinavia, Iceland and Alaska.
“You can also clearly see what happened in the XNUMXth century, and what stands out particularly, whether you consider each ice cap or all seven, is the unusual warming of the last fifty years. Nothing like this is found for earlier periods, even for the medieval warming period. The unusual oxygen isotope values therefore indicate that things are changing dramatically.
The isotopic data is clear in all the ice cores, but the most striking data is the appearance in the Quelccaya ice cap, which has receded in recent years, of non-fossilized plants, which normally grow in swamps.
Since their discovery in 2002, researchers have found twenty-eight places bordering the ice cap where these ancient plants have been exposed. Dating using carbon-14 reveals that these plants are between five thousand and six thousand years old. “It follows that the climate at the ice cap has never been warmer than it is today for the past five thousand years or more. If it had been warmer, these plants would have decomposed. "
According to the researchers, the great climate change that occurred some five thousand years ago in the tropics likely caused a cooling in these regions as the ice sheet expanded and covered the plants. The fact that they are now exposed to light indicates that the opposite is happening now: significant warming is causing the ice cap to melt rapidly.
Glaciers in the tropics, Professor Thompson said, are a warning system for the global climate because they respond to most of the major climatological variables: temperature, precipitation, clouds, humidity and solar radiation. “This shows us that our climate (…) can change abruptly due to either natural or man-made forces. If what happened five thousand years ago were to happen today, it would have far-reaching socio-economic implications for our entire planet. "