Global Temperature Reconstruction Over Last 24,000 Years Show Today’s Warming “Unprecedented”

Future Earth Global Warming

The University of Arizona team created maps of global temperatures for each 200-year interval since the last ice age.

A University of Arizona-led effort to reconstruct Earth’s climate since the last ice age, about 24,000 years ago, highlights the main drivers of climate change and how far out of bounds human activity has pushed the climate system.

The study, published Wednesday (November 10, 2021) in Nature, has three main findings: 

  • It verifies that the main drivers of climate change since the last ice age are rising greenhouse gas concentrations and the retreat of the ice sheets.
  • It suggests a general warming trend over the last 10,000 years, settling a decade-long debate the paleoclimatology community about whether this period trended warmer or cooler.
  • The magnitude and rate warming over the last 150 years far surpasses the magnitude and rate of changes over the last 24,000 years.

“This reconstruction suggests that current temperatures are unprecedented in 24,000 years, and also suggests that the speed of human-caused global warming is faster than anything we’ve seen in that same time,” said Jessica Tierney, a UArizona geosciences associate professor and co-author of the study.

Tierney, who heads the lab in which this research was conducted, is also known for her contributions to the Intergovernmental Panel on Climate Change reports and climate briefings for the U.S. Congress.

“The fact that we’re today so far out of bounds of what we might consider normal is cause for alarm and should be surprising to everybody,” said lead study author Matthew Osman, a geosciences postdoctoral researcher at UArizona.

Global Average Surface Temperature Curve

Global average surface temperature since the last ice age 24,000 years ago. Time is stretched for the past 1000 years to visualize recent changes. Credit: Matthew Osman

An online search of “global temperature change since the last ice age” returns a graph of global temperature change over time that was created eight years ago.

“Our team’s reconstruction improves on that curve by adding a spatial dimension,” Tierney said.

The team created maps of global temperature changes for every 200-year interval going back 24,000 years.

“These maps are really powerful,” Osman said. “With them, it’s possible for anyone to explore how temperatures have changed across Earth, on a very personal level. For me, being able to visualize the 24,000-year evolution of temperatures at the exact location I’m sitting today, or where I grew up, really helped ingrain a sense of just how severe climate change is today.”

Global Temperature Maps

These maps show global average surface temperature at different periods in Earth’s history going back 24,000 years. The darker the shade of blue, the colder the temperature compared to today. Credit: Matthew Osman

There are different methods for reconstructing past temperatures. The team combined two independent datasets – temperature data from marine sediments and computer simulations of climate – to create a more complete picture of the past.

The researchers looked at the chemical signatures of marine sediments to get information about past temperatures. Because temperature changes over time can affect the chemistry of a long-dead animal’s shell, paleoclimatologists can use those measurements to estimate temperature in an area. It’s not a perfect thermometer, but it’s a starting point.

Computer-simulated climate models, on the other hand, provide temperature information based on scientists’ best understanding of the physics of the climate system, which also isn’t perfect.

The team decided to combine the methods to harness the strengths of each. This is called data assimilation and is also commonly used in weather forecasting.

“To forecast the weather, meteorologists start with a model that reflects current weather, then add in observations such as temperature, pressure, humidity, wind direction, and so on to create an updated forecast,” Tierney said.

The team applied this same idea to past climate.

“With this method, we are able to leverage the relative merits of each of these unique datasets to generate observationally constrained, dynamically consistent, and spatially complete reconstructions of past climate change,” Osman said.

Now, the team is working on using their method to investigate climate changes even further in the past.

“We’re excited to apply this approach to ancient climates that were warmer than today,” Tierney said, “because these times are essentially windows into our future as greenhouse gas emissions rise.”

Reference: “Globally resolved surface temperatures since the Last Glacial Maximum” by Matthew B. Osman, Jessica E. Tierney, Jiang Zhu, Robert Tardif, Gregory J. Hakim, Jonathan King and Christopher J. Poulsen, 10 November 2021, Nature.
DOI: 10.1038/s41586-021-03984-4

The study also included co-authors Jonathan King from the UArizona geosciences department, Jiang Zhu from the Climate and Global Dynamics Laboratory at the National Center for Atmospheric Research, Robert Tardif and Gregory J. Hakim from the University of Washington, and Christopher J. Poulsen from the University of Michigan, Ann Arbor.

10 Comments on "Global Temperature Reconstruction Over Last 24,000 Years Show Today’s Warming “Unprecedented”"

  1. “It SUGGESTS a general warming trend over the last 10,000 years, settling a decade-long debate [sic] the paleoclimatology community about whether this period trended warmer or cooler.”

    A ‘suggestion’ is unlikely to settle anything. However, it is really naive to believe that anything in science is ever settled. Scientists are still testing Einstein’s theories of relativity after more than 100 years.

    What happened to the Holocene Climatic Optimum? Everyone else was wrong, based on a ‘suggestion?’ It looks like the Medieval Warm Period was also cut out due to the choice of where to splice data and change time scales. The change in time scales also precludes readers from making their own assessments about rates of warming.

    It is unwarranted to claim some recent event is “unprecedented” unless there is a significant difference. That is difficult to assess because short-term or transient events in the past can be filtered out by the decrease in temporal and temperature resolutions. An objective researcher would apply a low-pass filter to recent data to make it comparable to the historical data. It is a serious procedural mistake to splice historical proxy data to modern instrumental data. The question is, “Was this done out of ignorance, or to fit an agenda?”

    Yet another poor quality piece of published research. It gives me pause about the reliability of the original data on which the conclusions are based.

  2. BS, the world is not hotter today than any other time in the past 24,000 years. Just wait a few months and try telling the world that it’s hotter now than in the past, when the temperatures drop and it’s snowing outside, only people trapped in the Khazarian Deep State Matrix will believe anything you say.

  3. GREG MALINOWSKI | November 12, 2021 at 9:40 am | Reply

    I love these folks, like the ones on the stern of the Titanic, “Sinking? My part of the ship is completely out of the water, we can’t be sinking!”

  4. Deniers are quite uninformed of basic co2 methanes levels and their effects. Yes it is warming quickly. Yes it will still be cold often for centuries. We are now at the co2 methane levels of five million years ago which means over the next several centuries sea levels will return 130 ft higher so to match co2 / methane levels of five million years ago. That is not the end of the world but goodbye to coastal areas over time. Deniers claim that scientists deny co2 and methane levels change temp and climate. Not so , that is proven by simply looking at the past correlation between co2 / methane levels and sea levels and temps. But we are talking centuries here not 13 years

  5. Peter Newsone | July 18, 2022 at 6:24 am | Reply

    Why would the layman believe the climate alarmists .. the scientists still in debate, every projected date/deadline has been wrong .. Australians were “guaranteed” that our dams would run empty by 2006 and never refill .. surprise surprise… we spent billions on desalination plants on this shoddy advice and now we have floods regularly and not enough dam space .people drowning in floods that were supposedly not going to happen … . l am sick of scientist opinions and be projections .. the record keeping is also adjusted by the record keepers to suit their beliefs .. the crisis we have is the alarmism created by all this and the distraction it causes from the genuine existential threats ..

  6. Fujikane masakazu | January 9, 2023 at 11:47 pm | Reply

    Where is hypsithermalperiod (7000-5000 years ago)? it was 2-4 degree higher than now.

  7. I think that science is propaganda

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