As extreme temperatures grip various parts of the Earth, many people seek to understand the historical context and ask when such heatwaves occurred before. While 2023 has witnessed some of the hottest days in modern measurements, scientists have looked back even further to estimate past global temperatures. As a paleoclimate scientist, I analyze temperature records from natural archives to provide valuable insights into the Earth’s climate history. However, when it comes to claims of daily temperatures reaching a 100,000-year high, it is essential to acknowledge that detailed temperature records do not extend that far back. Nonetheless, we can confidently state when the Earth was last in a state as hot as today.
The New Climate State
Several years ago, scientists determined that Earth had entered a new climate state not seen in over 100,000 years. This conclusion was based on a climate assessment report by the Intergovernmental Panel on Climate Change (IPCC) in 2021. With temperatures already more than 1 degree Celsius warmer than preindustrial times and elevated greenhouse gas levels, the Earth was experiencing a multi-century global warming of 1 C and higher. Even under the most optimistic scenarios for the future, it is likely that average global temperatures will remain at least 1 C above preindustrial levels for centuries to come.
Estimating Past Temperatures
To reconstruct temperatures from periods before the use of thermometers, paleoclimate scientists rely on data stored in various natural archives. Sediment cores from lake beds and ocean floors are particularly valuable sources of information. However, these records have limitations, such as potential mixing of sediment and imprecise timelines, making it challenging to compare them with short-term temperature extremes.
Looking Back Tens of Thousands of Years
The Earth’s average global temperature has historically fluctuated between glacial and interglacial conditions, influenced by changes in Earth’s orbit and greenhouse gas concentrations. Currently, we are in an interglacial period that began approximately 12,000 years ago. During this period, the global temperature may have peaked around 6,000 years ago, but it likely did not exceed the 1 C global warming level. To find a time as warm as today, we must look even further back to the previous interglacial period, around 125,000 years ago, where evidence suggests temperatures were no more than 1.5 C above preindustrial levels.
The Future of Climate Change
Without significant and sustained reductions in greenhouse gas emissions, Earth is projected to reach temperatures of approximately 3 C above preindustrial levels by the end of the century. Such a scenario would take us back millions of years, to the previous geologic epoch, the Pliocene. At that time, Earth’s climate resembled a distant relative of the one that fostered the rise of agriculture and civilization.
As Earth experiences scorching heatwaves in 2023, it is crucial to understand the historical context of such extreme temperatures. While daily temperature records from 100,000 years ago cannot be definitively confirmed, scientists can confidently state that Earth’s current climate state is unlike any observed in the past 100,000 years. With the increasing impact of human-induced climate change, it is imperative to address greenhouse gas emissions to avoid potential catastrophic consequences and maintain a sustainable climate for future generations.