The hot statement in this week’s landmark Intergovernmental Panel on Climate Change (IPCC) report is This is especially worrying given the cautious language peculiar to science. The first consensus of the 234 authors of the document is that it is “clear” that humans burn fossil fuels to cause climate change.In fact, the reconstruction of the data in the report shows that the average surface temperature of the earth has probably not been this warm for a long time. About 125,000 years later [see “Change in Global Surface Temperature”].
The latest IPCC report pulls Point out that there is no ambiguity in describing the consequences of increased greenhouse gas emissions Kincob, A climate scientist at Georgia Institute of Technology and one of the lead authors of the assessment, in a pre-release briefing for reporters. Compared with past IPCC reports, Cobb and her co-authors concluded that climate change has caused extreme heat waves, droughts, heavy rains, and tropical cyclones around the world. In all possible emission scenarios studied, the temperature will rise to at least 2050 and may exceed 1.5 degrees Celsius by 2040. However, if emissions reach net zero by 2050-which means that any released greenhouse gases will be removed from the atmosphere to balance the amount of greenhouse gases-over the course of this century, warming can still be limited to 1.5 degrees Celsius.
This Nearly 4,000 pages of documentsMore than 14,000 studies have been cited and this is the first major assessment of the state of climate science by the IPCC since 2013. The certainty of the report is based not only on a better understanding of the Earth’s climate system, but also on the investigation of its climate in the past. Data from corals, tree rings, cores extracted from ice or ocean sediments, and other sources enable paleoclimate researchers such as Cobb to transcend modern records and enter the ancient world, providing important insights for today’s climate science and prediction. Scientific american Discussed with Cobb the role of paleoclimate data in improving the new IPCC report and the importance of providing context for the current global warming.
[An edited transcript of the interview follows.]
Why is it important to look back at the past climate?
Given that the climate records measured by instruments usually only date back 50 years-sometimes 100 or 150 years-we cannot truly capture the full range of natural changes in the Earth’s climate system. What we can do with paleoclimate archives is to go back to the past. Now, we have enough records in many locations around the world to perform large-scale averaging-this type allows us to directly compare with what is happening on Earth today. It is important to provide background information about how fast things are changing today and how unusual it is.
How is paleoclimate research used in this new report?
Since the first IPCC assessment in 1990, paleoclimate research has been a part of every IPCC assessment. The difference here is that instead of categorizing these evidences into separate chapters, we try to integrate these evidences into all aspects of the report. Climate scientists in all disciplines now understand the wealth of information provided by paleoclimate sources. In recent decades, the field has matured to provide quantitative information suitable for the most common types of quantitative analysis in current climate change research.
Is there any precedent in the geological record for the climate change we are seeing today?
It is interesting to look at the time of the last interglacial period about 125,000 years ago. Our best estimate of the temperature increase during this time is about 1 to 2 degrees Celsius-which is no different from where we stopped today, about 1 degree Celsius higher than the pre-industrial period. At the time, this increase was caused by changes in the Earth’s orbit relative to the sun, and the warming lasted for thousands of years, causing the Greenland ice sheet to melt and causing global sea levels to rise by 5 to 10 meters. These numbers are a huge exclamation point, indicating where our planet is in the not-too-distant geological history, and the long-term direction of development as the earth responds adequately to the levels of warming we are already at.
However, none of the Earth’s past warm periods is a suitable analogy as we see it today. The speed of what we are doing now tends to distinguish current climate change from such large-scale changes that have occurred in the past on longer time scales and caused by natural climate drivers.
Climate sensitivity essentially refers to how much warming will occur for every additional unit of carbon dioxide in the atmosphere.For a given CO, higher climate sensitivity means more warming2 Increase and vice versa. This is one of the uncertainties about the impact of future emissions, but compared with previous reports, this report has significantly reduced its scope.
Paleoclimate science can promote dialogue around climate sensitivity by studying the temperature response to past CO2 changes2, Based on data describing the Earth’s past climate conditions.
Like my colleague Jessica Tierney Work hard at the University of Arizona Compile the global temperature database of the last ice age, About 20,000 years ago, and used it to estimate the global cooling during that time. We know CO2 Very good, so with these two numbers, she and her co-authors were able to calculate an estimate of climate sensitivity.
The report predicts that even if we succeed in limiting warming to 1.5 degrees C. The sea level will continue to rise until 2050. why is that?
So far, the heat that we have baked into the atmosphere has penetrated into the ice sheet. The adjustment to the excessive heat that we have caused — and will continue to cause — will be imprinted in the continuous slow melting of these huge ice sheets, for centuries or even thousands of years.
The good news is that if we implement deep and sustained reductions in greenhouse gas emissions now, we will see the benefits of doing so in the form of reduced sea level rise later in this century. Where do we want the sea level to fall? Do we want to give future generations as much time as possible to adapt? These are the problems we face in this decade and the next.
Are there any other processes that are basically “locked up” for a long period of time?
Generally speaking, ocean impacts will take longer to reverse. An important effect is ocean acidification, the characteristic of carbon stored in the ocean. We have reduced the chemical composition of the upper ocean to 2000 meters-in some places almost half its depth.The carbon will not magically come out all at once; it will appear in the form of these high CO2 The water is exposed to an atmosphere with a lower carbon dioxide content on the surface2We must wait for this exchange to happen, because deep water must surface again. This will be a relatively slow process.
This does not conflict with one of the core messages of the report, which is that when we reach net zero emissions, we will begin to see global warming itself almost immediately and apparently stabilized if not reversed. Many effects directly related to global surface temperature, such as heat waves, may be one of the first to respond.
How can paleoclimate research continue to increase our understanding of climate change?
Reviewing paleoclimate records can help us understand how extreme climates or cyclic groups have evolved in the recent past, and how they might change with climate change. It is becoming increasingly clear that these methods are extremely relevant to our climate future. We can turn to archives of past extreme events—whether it’s droughts, extreme rains, tropical cyclones—or natural climate cycles to learn more about their natural changes over the past few centuries to thousands of years. An example is the El Niño event, which is the warming phase of the natural climate cycle that occurs in the tropical Pacific. In the past 70 years, we have really only seen a few people—10, give or receive. But by looking at the paleoclimate archives of El Niño events, we can analyze hundreds of events over the past few thousand years.Just last year, we published a paper record The intensity of El Niño has increased in recent decades, Compared with the pre-industrial era.
Can we learn from the insights of climate optimism these days?
I am a little relieved to see that the rest of the world can reach the level of consciousness I have had in the past five to eight years. When you have to keep up with the pace of scientific development in your daily work, you can digest it in real time. It feels like I have lost a little weight now—at least the rest of the world knows what I’m doing at the moment. This is a huge relief.
I hope that the new understanding will drive the necessary actions to take this deep and sustained path of emission reduction, limit warming and retain the right to cool down later in this century. This is what I strive for.