Reconstructing global climate through Earth's history

Date:
August 13, 2020
Source:
Syracuse University
Summary:
Accurate temperature estimates of ancient oceans are vital because
they are the best tool for reconstructing global climate conditions
in the past. While climate models provide scenarios of what the
world could look like in the future, paleoclimate studies (study
of past climates) provide insight into what the world did look
like in the past.



FULL STORY ==========================================================================
A key component when forecasting what the Earth's climate might look like
in the future is the ability to draw on accurate temperature records of
the past.

By reconstructing past latitudinal temperature gradients (the difference
in average temperature between the equator and the poles) researchers can predict where, for example, the jet stream, which controls storms and temperatures in the mid-latitudes (temperate zones between the tropics
and the polar circles), will be positioned. The trouble is, many of
the existing data are biased toward particular regions or types of environments, not painting a full picture of Earth's ancient temperatures.


========================================================================== Researchers from the Department of Earth and Environmental Sciences,
including Emily Judd '20 Ph.D., Thonis Family Assistant Professor Tripti Bhattacharya and Professor Linda Ivany, have published a study titled,
"A dynamical framework for interpreting ancient sea surface temperatures,"
in the journal "Geophysical Research Letters," to help account for the
offset between location-biased paleoclimate data and the 'true' average temperature at a given latitude through Earth's history. Their work was
funded by the National Science Foundation.

According to Judd, accurate temperature estimates of ancient oceans are
vital because they are the best tool for reconstructing global climate conditions in the past, including metrics like mean global temperature
and the latitudinal temperature gradient. While climate models provide scenarios of what the world could look like in the future, paleoclimate
studies (study of past climates) provide insight into what the world
did look like in the past. Seeing how well the models we use to predict
the future can simulate the past tells us how confident we can be in
their results. It is therefore of utmost importance to have thorough, well-sampled data from the ancient past.

"By understanding how latitudinal temperature gradients have changed
over the course of Earth's history and under a variety of different
climate regimes, we can start to better anticipate what will happen in
the future," says Judd.

To determine ancient temperatures, geologists study proxies, which are
chemical or biological traces that record temperatures from sedimentary deposits preserved on the sea floor or continents. Due to the recycling of ancient seafloor into the Earth's mantle, there is an 'expiration date'
on the availability of seafloor data. Most ancient temperature proxies therefore come from sediments that accumulated on continental margins
or in shallow inland seas where records can persist for much longer.

Judd, Bhattacharya and Ivany use temperature data from modern oceans
to reveal consistent, predictable patterns where the ocean surface is
warmer or cooler, or more or less seasonal, than otherwise expected at
that latitude.

"The biggest offsets happen to be in the two settings that are most
represented in the geologic past," says Ivany. "Knowing how those
regions are biased in comparison to the global mean allows researchers
to better interpret the proxy data coming from the ancient Earth."
Data from shallow, semi-restricted seas (e.g., the Mediterranean and
Baltic Seas) show that sea surface temperatures are warmer than in the
open ocean. As a result, a key finding of their paper theorizes that
estimates of global mean temperature from the Paleozoic Era (~540-250
million years ago), a time when the majority of data come from shallow
seas, are unrealistically hot.

Even in the more recent geologic past, the overwhelming majority of
sea surface temperature estimates come from coastal settings, which
they demonstrate are also systematically biased in comparison to open
ocean temperatures.

In order to have a more accurate record of average ocean temperature
at a given latitude, Bhattacharya says researchers must account for
the incomplete nature of paleotemperature data. "Our work highlights
the need for the scientific community to focus sampling efforts on under-sampled environments," says Bhattacharya. "New sampling efforts
are essential to make sure we are equally sampling unique environmental settings for different intervals of Earth's history." According to
Judd, the paleoclimate community has made major advances toward
understanding ancient climates in the past few decades. New, faster,
and cheaper analytical techniques, as well as a surge in expeditions
that recover ocean sediment cores, have led to massive compilations of
ancient sea surface temperature estimates. Despite these advancements,
there are still significant disagreements between temperature estimates
from different locations within the same time interval and/or between temperature estimates and climate model results.

"Our study provides a framework within which to reconcile these
discrepancies," says Judd. "We highlight where, when and why temperature estimates from the same latitudes may differ from one another and compare different climate models' abilities to reconstruct these patterns. Our
work therefore lays the groundwork to more holistically and robustly reconstruct global climate through Earth's history."

========================================================================== Story Source: Materials provided by Syracuse_University. Original written
by Dan Bernardi.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Emily J. Judd, Tripti Bhattacharya, Linda C. Ivany. A Dynamical
Framework
for Interpreting Ancient Sea Surface Temperatures. Geophysical
Research Letters, 2020; 47 (15) DOI: 10.1029/2020GL089044 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200813152244.htm

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