M: Lak yes. Even under the most optimistic future scenarios—in which humans stop burning fossil fuels and reduce other greenhouse gas emissions—the average global temperature will likely remain at least 1°C above pre-industrial temperatures, and possibly much more, for hundreds of years.
By Darrell Kaufman, Professor of Earth and Environmental Sciences, Northern Arizona University
As scorching heat prevails across large parts of the planet, many people try to put the extreme temperatures into context and ask: When has it ever been this hot before?
Globally, 2023 saw some of the hottest days in modern records, but what about further back, before weather stations and satellites?
Some media reported that daily temperatures reached a 100,000-year high.
As a paleoclimate scientist who studies past temperatures, I understand where this claim is coming from, but I cringe at the inaccurate headlines. While this claim may well be true, there are no detailed temperature records spanning 100,000 years, so we don't know for sure.
Here's what we can say with confidence about when Earth was last this hot.
This is a new climate
מדענים הגיעו למסקנה לפני כמה שנים שכדור הארץ נכנס למצב אקלימי חדש שלא נראה יותר מ-100,000 שנה. כפי שעמיתנו מדען האקלים ניק מקיי ואני דנו לאחרונה במאמר בכתב עת מדעי, מסקנה זו הייתה חלק מדו"ח הערכת אקלים שפורסם על ידי הפאנל הבין-ממשלתי לשינוי האקלים (IPCC) בשנת 2021.
The Earth was already more than one degree warmer than in pre-industrial times, and levels of greenhouse gases in the atmosphere were high enough to ensure that temperatures would remain high for a long time.
A time series chart shows a peak about 125,000 years ago and indicates today's glaciers, showing temperatures close to the 1C warming level.
Earth's average temperature has risen 1.8 degree Celsius (100,000 Fahrenheit) above the pre-industrial baseline. This new climate state will probably last for hundreds of years as the warmest period in more than 1850 years. The chart shows different reconstructions of temperature over time, with temperatures measured since 2300 and projected to 2022 based on an intermediate emissions scenario. DS Kaufman and NP McKay, XNUMX, and published data sets, courtesy of the author.
Even under the most optimistic future scenarios—in which humans stop burning fossil fuels and reduce other greenhouse gas emissions—the average global temperature will likely remain at least 1°C above pre-industrial temperatures, and possibly much more, for centuries.
This new climate state, characterized by global warming of 1°C or more, can be reliably compared with temperature reconstructions from the very distant past.
How we estimate past temperature
To reconstruct temperatures from pre-thermal times, paleoclimate scientists rely on information stored in a variety of natural archives.
The most common thousands-year-old archive is found at the bottom of lakes and oceans, where a variety of biological, chemical and physical evidence offers clues to the past. These materials accumulate continuously over time and can be analyzed by extracting a sediment core from the lake floor or ocean floor.
Two female scientists on a boat examine a sediment core, with the layers clearly visible. Scientist Ellie Brodman of the University of Arizona holds a sediment core from the bottom of a lake on Alaska's Kenai Peninsula. Emily Stone
These sediment-based records are rich sources of information that have allowed paleoclimate scientists to reconstruct past global temperatures, but they have important limitations.
First, bottom currents and burrowing organisms can mix the sediments, obscuring any short-term temperature jumps. Second, the timeline of each record is not precisely known, so when multiple records are averaged together to estimate past global temperature, fine-scale fluctuations can be discarded.
For this reason, paleoclimate scientists are reluctant to compare the long-term record of past temperatures with short-term extremes.
Looking back tens of thousands of years
The Earth's average global temperature fluctuates between glacial and interglacial conditions in cycles lasting about 100,000 years, mainly by slow and predictable changes in the Earth's orbit with accompanying changes in the concentrations of greenhouse gases in the atmosphere. We are currently in an interglacial period that began about 12,000 years ago, when the ice sheets retreated and greenhouse gases rose.
בהסתכלות על התקופה הבין-קרחונית בת 12,000 השנים, הטמפרטורה הגלובלית הממוצעת על פני מאות שנים אולי הגיעה לשיאה לפני כ-6,000 שנה, אך ככל הנראה לא עברה את רמת ההתחממות הגלובלית של 1 מעלות צלזיוס באותה נקודה, על פי דו"ח ה-IPCC. מחקר אחר מצא כי הטמפרטורות הממוצעות העולמיות המשיכו לעלות לאורך התקופה הבין-קרחונית. זהו נושא למחקר פעיל.
This means we have to look further back to find a time that could have been as warm as today.
The last glacial episode lasted almost 100,000 years. There is no evidence that long-term global temperatures reached the pre-industrial baseline at any time during this period.
If we look even further back, to the previous interglacial period, which peaked about 125,000 years ago, we find evidence of warmer temperatures. The evidence suggests that the long-term average temperature was probably no more than 1.5 degrees Celsius above pre-industrial levels – not much more than the current level of global warming.
What now?
Without a rapid and sustained reduction in greenhouse gas emissions, the Earth is currently on track to reach temperatures of about 3 degrees Celsius above pre-industrial levels by the end of the century, and possibly quite a bit more.
At this point, we would have to look back millions of years to find a climate with such warm temperatures. This would take us back to the previous geological period, the Pliocene, when Earth's climate was a distant relative of that which supported the rise of agriculture and civilization.
For an article in The Conversation
More of the topic in Hayadan:
Comments
I have a feeling that even a billion years won't be enough for you.
In ecological and certainly geological terms, 100,000 years is like the blink of an eye. In short, the current warming is negligible compared to the situation during most of the existence of life on Earth.
In a hundred thousand years there were several cycles of ice ages and warm periods, and there is also a limit to the ability of the proxies. If they could check even 200 thousand years they would check.
Why stop at 100 thousand years? Why is this number better than 200 thousand?
I'm afraid the study is cherry-picking to express an opinion...