As the earth’s temperature continues to rise, the permaculture of the Arctic permafrost is no longer guaranteed.But according to the Intergovernmental Panel on Climate Change (IPCC), it is still unclear to what extent the degradation of the so-called permafrost will exacerbate climate change Sixth Assessment Report, Released this week. This uncertainty has left researchers with a frustrating hole in their climate predictions.
Permafrost cover Quarter Land in the northern hemisphere and surrounding shops 1.5 trillion metric tons Organic carbon is twice that of the current earth’s atmosphere. Most of this carbon is the remains of ancient life wrapped in frozen soil for hundreds of thousands of years.
In recent decades, permafrost has melted because global warming is mainly caused by carbon dioxide released into the atmosphere by burning fossil fuels.Arctic warming is rising Twice the global average According to the US National Oceanic and Atmospheric Administration, since 2000. As this increase accelerates the melting of permafrost, the organic carbon contained therein decomposes and releases carbon dioxide, exacerbating climate change.
But climate scientists are not sure how much carbon permafrost will release and when, this is reflected in the broad estimates provided by the IPCC report this week. This uncertainty hinders the prediction of climate change and makes it more difficult to know whether countries around the world are expected to achieve the 2015 targets set to limit global warming. Paris Agreement. The formulation of policies to achieve these goals depends on an accurate understanding of the amount of carbon dioxide that enters the atmosphere each year.
Most existing climate models currently do not consider carbon released from permafrost in their simulations. On the contrary, the latest IPCC report provides the best estimate of the range of carbon that permafrost may emit.Then consider this range when estimating the world’s remaining carbon budget-the amount of carbon dioxide2 It’s still possible to emit – in order to meet the goals of the Paris Agreement, say Charlie Cowan, A carbon cycle scientist at Lawrence Berkeley National Laboratory and one of the main authors of the report. He said that although it is not ideal, this approach “reflects the urgency of the climate crisis.” “We don’t have time to find the perfect solution. We need to act based on the knowledge we have.”
At the same time, researchers are trying to better understand the contribution of permafrost to global warming. The key is the earth’s carbon cycle, in which carbon is exchanged between land, water and air. In the warming Arctic, two opposing effects are changing this cycle. As the soil thaws, bacteria, fungi, and other microorganisms living in the soil consume the exposed organic matter and release carbon into the atmosphere. Microbial communities can thrive better in warm Arctic regions, thereby increasing their numbers and appetite. This may form a so-called feedback loop: climate change causes more carbon dioxide to be released, which worsens the problem on a global scale, thereby triggering more carbon release. However, plants generally grow better in warm temperatures and carbon-rich air. This growth absorbs more carbon from the air and deposits it in the soil when the plant dies.Therefore, as the earth’s permafrost warms, “you will ask,’Who won?’ We can’t know immediately,” said Ted Shure, Professor of Northern Arizona University, studies Arctic ecosystems.
For the past 20 years, Schuur has operated a research site near Denali National Park in Alaska, trying to determine the winner by monitoring the exchange of carbon dioxide between soil and air.He reported some worrying things in the magazine this spring JGR Bio-Earth Science: Soil microorganisms are winning, which means that the small area around the Schuur research site is a net Source of Carbon Monoxide2.
At this point, “it’s hard to imagine that plant growth can exceed the loss of carbon in permafrost soil,” Koven said. But in order to better determine the amount of permafrost carbon that may be released throughout the 21st century, “there is still a lot of work to be done.”
And other CO2-Monitoring sites have also recently shown that microbes are winning-for example, in Survey results announced this month exist Environmental Research Letters— There are too few sites to confidently represent all the permafrost regions on the earth, which span approximately 22 million square kilometersJennifer Watts, an Arctic Systems Researcher at the Woodwell Climate Research Center in Falmouth, Massachusetts, said that few of these research sites are located in Siberia, which is the largest permafrost region in the world, making it a “black box.” .
The harsh, remote terrain of the Arctic makes it challenging for researchers to take risks and build more sites. One possible remedy is to use satellites to observe the melting permafrost from a distance.Scientists have used satellites to determine Vegetation coverage has been increasing In most parts of the Arctic, even remote monitoring of carbon emissions requires more technical skills.
Sparse sampling is not the only reason for the uncertainty in the contribution of permafrost melting to climate change. Arctic scientists also continue to discover shocking new twists in the carbon cycle story. In 2019, Watts and other scientists Natural climate change Microorganisms in many research sites are still somewhat active Even in winter, Thereby releasing a certain amount of carbon dioxide throughout the year.Separately, in Natural Earth Science The following year, Schuur, Koven, and other researchers tied up the melting lake-expanding the melting pool from the melting ice-rich permafrost-Release methane bubbles, A carbon compound that has a stronger greenhouse effect than carbon dioxide. “Without these bubbles, you would underestimate the carbon feedback,” said Katie Walter Anthony, Professor of Ecosystem Ecology, University of Alaska Fairbanks and co-author of Melting Lake Research.
Watts said that even today, the release of methane from the warming of the Arctic remains “a huge question mark.” “We know that there is methane. We don’t know how much there is, and we absolutely don’t know what the future will look like.”
Although the global average temperature has risen by more than One degree Celsius Koven said that from a pre-industrial level, “this is relatively small compared to the possible changes waiting for us.” To better understand the future impact of global warming on permafrost, the preferred strategy for climate scientists is to examine Its a warmer past. Over the past few million years, the temperature has occasionally been slightly higher than today. “Every warm period is a great natural experiment,” said Alberto Reyes, An associate professor at the University of Alberta, who studies how ancient permafrost reacted to these past warm periods.
This spring, Reyes and others analyzed Canadian Arctic and subarctic cave deposits, such as rhyolites and stalagmites, and determined Arctic permafrost soils Defrosted a lot In some ancient warm times.But based on Record from ice core Judging from the Antarctic and Greenland ice sheets that contain bubbles from the distant past, the peaks of carbon dioxide or methane in the atmosphere do not seem to follow.
“Where are those greenhouse gases?” Reyes said. The answer is not necessarily that they were not released from the melting permafrost. The oceans of ancient times had more time to absorb the carbon dioxide released by permafrost than this time. Today’s level is much higher than the level of the past two million years, and it is rising at an alarming rate. Faster speed“So far, we have promoted the system,” he said. “Humans have created a non-simulated condition.”