The Climate is changing all the time for eons of years long before humans appeared!
Celsius surface temperatures in the 30s or even 40s were quite normal! Warmer periods were longer and dominated colder periods.
According to this new study past, similar studies have probably underestimated the global mean surface temperatures.
I kind of doubt and disagree with the conclusion that "CO2 is the dominant control on Phanerozoic climate". CO2 is a trace gas measured in parts per million! What about e.g. cloud formation? We still know very little about e.g. cloud formation! Cloud formation was not even considered by these scientists!
Global Warming is a hoax and Climate Change is a religion!
Keep in mind: The reconstruction of air or surface temperatures via proxy data is controversial and not necessarily accurate or reliable. Similar climate models!
"A new study co-led by the Smithsonian and the University of Arizona offers the most detailed glimpse yet of how Earth’s surface temperature has changed over the past 485 million years. In a paper ... produce a curve of global mean surface temperature (GMST) across deep time—the Earth’s ancient past stretching over many millions of years. The new curve reveals that Earth’s temperature has varied more than previously thought over much of the Phanerozoic Eon, the past 540 million years of geologic time when life has diversified, populated land and endured multiple mass extinctions. The curve also confirms that Earth’s temperature is strongly correlated [???] to the amount of carbon dioxide in the atmosphere. ..."
"To predict how our planet might change in the future, scientists need an accurate record of the planet’s past. But deducing things like temperature changes over eons can be tricky. All of the various proxies have their flaws, and they’ve sometimes come to starkly different conclusions. But now, by combining climate models with geological data, researchers have reconstructed the last 485 million years of global temperatures. ..."
"... Polar ice caps leave distinctive geological evidence that geologists can recover (3), which has allowed mapping of how extensive these frozen regions were over the Phanerozoic Eon—the last 540 million years during which animals and plants evolved. This record shows a cycle between “icehouse” periods with large permanent ice caps and “greenhouse” periods without them. The present-day Earth is an icehouse, and it has been for the past 34 million years. The current average surface temperature is around 15°C. But were previous icehouse periods also at this temperature, and how hot were the greenhouse periods? Knowing the past temperature of Earth helps us better understand future climate changes, but measuring it is difficult. Ice cap locations depend on the positioning of the continents, which has changed substantially over time. The sparse geological record causes frequent revision of timing and extent of past glaciation. ..."
From the editor's summary and abstract:
"Editor’s summary
Understanding how global mean surface temperature (GMST) has varied over the past half-billion years, a time in which evolutionary patterns of flora and fauna have had such an important influence on the evolution of climate, is essential for understanding the processes driving climate over that interval. Judd et al. present a record of GMST over the past 485 million years that they constructed by combining proxy data with climate modeling (see the Perspective by Mills). They found that GMST varied over a range from 11° to 36°C, with an “apparent” climate sensitivity of ∼8°C, about two to three times what it is today. ...
Abstract
INTRODUCTION
A long-term geological record of global mean surface temperature (GMST) is important for understanding the history of our planet and putting present-day climate change into context. Such a record is necessary for constraining the relationship between climate and other aspects of the Earth system, including the evolution and extinction of life, and the chemistry of the atmosphere and oceans. Further, quantifying the relationship between GMST and atmospheric carbon dioxide (CO2) concentrations can refine our understanding of Earth’s climate sensitivity and improve future predictions under anthropogenic warming.
RATIONALE
Although several Phanerozoic (the last 539 million years) temperature reconstructions exist, during the intensively studied Cenozoic Era (the last 66 million years), they are colder and less variable than individual estimates from key time periods, particularly during ice-free (greenhouse) intervals. This discrepancy suggests that existing Phanerozoic temperature records may underestimate past temperature change, and merits further investigation using a new approach.
RESULTS
Here, we present PhanDA, a reconstruction of GMST spanning most of the Phanerozoic Eon. PhanDA was created using data assimilation, a method that statistically integrates geological data with climate model simulations. PhanDA indicates that Earth’s temperature has varied between 11° and 36°C over the past 485 million years. This range is larger than previous reconstructions; however, PhanDA agrees well with independent GMST estimates from the Cenozoic, providing confidence in its larger dynamical range.
PhanDA reveals key features in the relationship between GMST and the pole-to-equator temperature gradient, including polar amplification (i.e., larger temperature changes at high latitudes) and a shallowing of the gradient with increasing GMST. Tropical temperatures range between 22° and 42°C, refuting the idea of a fixed upper limit on tropical warmth and suggesting that ancient life must have evolved to endure extreme heat. We parse PhanDA into five climate states and find that overall, Earth has spent more time in warmer climate states than cold ones during the Phanerozoic.
There is a strong relationship between PhanDA GMST and CO2, indicating that CO2 is the dominant control on Phanerozoic climate. The consistency of this relationship is surprising because on this timescale, we expect solar luminosity to influence climate. We hypothesize that changes in planetary albedo and other greenhouse gases (e.g., methane) helped compensate for the increasing solar luminosity through time. The GMST-CO2 relationship indicates a notably constant “apparent” Earth system sensitivity (i.e., the temperature response to a doubling of CO2, including fast and slow feedbacks) of ∼8°C, with no detectable dependence on whether the climate is warm or cold.
CONCLUSION
PhanDA provides a statistically robust estimate of GMST through the Phanerozoic. We find that Earth’s temperature has varied more dynamically than previously thought and that greenhouse climates were very warm. CO2 is the dominant driver of Phanerozoic climate, emphasizing the importance of this greenhouse gas in shaping Earth history. The consistency of apparent Earth system sensitivity (∼8°C) is surprising and deserves further investigation. More broadly, PhanDA provides critical context for the evolution of life on Earth, as well as present and future climate changes."
ScienceAdvisor
PhanDA global mean surface temperature across the last 485 million years.
Fig. 2. Phanerozoic temperature history. PhanDA reconstructed GMST for the past 485 million years.
Black line shows the median, shading corresponds to the ensemble percentile.
Blue rectangles show the maximum latitudinal ice extent (2), and
orange dashed lines show the timing of the five major mass extinctions of the Phanerozoic (36).
