Visualizing the Rise in Global Temperatures Over the Past 20,000 Years

There is no denying that the climate has changed over the past 20,000 years. The amount of warming and cooling over this period is well documented, with some studies putting the global average temperature increase at 2°C. What is less well-known is how quickly global temperatures have risen and fallen by examining thousands of proxy records spanning thousands of years. These records show us that just like in modern times, global temperatures have been on a slow but steady rise over the past two millennia or so. What we can learn from these proxy records, is which ones we should pay attention to, as well as potential implications for future warming trends.

Understanding Past Warming And Cooling Trends

The first thing to understand about past warming and cooling trends is the variation in the amount of warming and cooling that occurred over time periods as short as a decade. Some proxy records spanning a few centuries can give a more nuanced view of past climate change. The tree-ring data from Central and South America, for example, show a period of Cooling from the 16th to 19th centuries, followed by a period of Warming from the 20th to 23rd centuries. Another proxy record that is useful for examining past warming and cooling trends is the dendrokine–chloropine record, which records the amount of CO2 in the atmosphere and the rate at which it is drawn down by trees and other plants.

Rising Temperatures Over The Past 20,000 Years

The period from the end of the last ice age through to the start of the Holocene age saw a long-term warming trend. This is evident from the fact that the global mean temperature at the end of the last ice age was about 8°C higher than it is today. The reason for this is that the Earth was significantly warmer than it is today during the last ice age. The last ice age ended about 18,000 years ago, and the current interglacial period began about 11,000 years ago.

As the climate changed, the amount of carbon dioxide in the air also changed, rising at a faster rate during the last ice age and falling during the current interglacial period. CO2 levels in the atmosphere have fluctuated over the past 2,000 years, but they are now at their highest recorded level. While the precise reasons for the past rise in CO2 remain a matter of debate, there is no doubt that rising CO2 has been a key factor in keeping the Earth’s temperature rise in check during the past two millennia.

Co2 And Temperature Relationship Over 20,000 Years

The increase in global average temperatures was accompanied by a rise in CO2 levels in the atmosphere. Using proxy records, we can examine how closely these two variables track each other over the past 20,000 years. We find that the amount of CO2 in the air increased by around 2 parts per million (ppm) from the end of the last ice age to the start of the Holocene age. This increase was accompanied by an increase in the rate at which the air was getting more CO2 from the Earth’s crust, which in turn led to an increase in global average temperatures of around 0.2°C. This is not a consistent relationship over time, however.

At certain times, particularly during the periods of rapid climate change that occurred between the end of the last ice age and the beginning of the current interglacial, the amount of CO2 in the air and the rate at which it was getting out of the ground were not closely related. A better match between CO2 and temperature would occur if the current period were separated from the past two millennia by a period of a relatively stable climate.

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