Just how significant are the temperatures that we are currently experiencing in the 21st century?
In this guide, we take a look at how warm climate and temperatures got on earth in the past, so we can put current climate into perspective.
Summary – How Warm Earth Got In The Past
- There’s a few different time periods throughout Earth’s past
- The last 20,000 years has been unusually stable compared to the rest of Earth’s history – the last 20,000 years is the period in which humans (in the form we know ourselves today) developed. About 20,000 years ago, we were coming out of an ice age, and the Earth has gradually warmed from -4.3 degrees celcius
- Prior to the last 20,000 years, up to about the last 3 million years, the world went through ice ages, composing of glacials (cooling) and interglacials (warming). Temperatures and the climate varied. Cooling was gradual, followed by a predictable warming period, before going into cooling again. The gap between the warmest and coldest temperatures could be sizeable
- Prior to 3 million years ago and up to about 40 million years ago, the Earth went through an extended ice age. Between about 12 to 25 million years ago, there was a period in that extended ice age where the temperature jumped up
- Going back 40+ million years ago, Earth’s climate and temperatures could be unpredictable, abrupt and extreme. There was thought to be a lot of fluctuation between the hottest and coldest temperatures. As one example, the global mean temperature about 65 millions years ago seems to have risen by as much as 5-8 °C (9-14 °F) to an average temperature as high as 23 °C (73 °F), in contrast to the global average temperature of today at just under 15 °C (60 °F)
- These temperatures of the past were all influenced by different factors at that specific time in Earth’s history (the orbit of the Earth in relation to the sun is one such factor)
- It’s worth noting that temperatures from the past are obtained from ancient samples such as shells from deep sea sediments, and ice cores (mainly from Antarctica and Greenland). So, their accuracy is dependent on the reliability of these types of samples
How Warm Is The Climate Right Now In The 21st Century?
- The change in global surface temperature up to 2019, relative to 1951-1980 average temperatures, is 0.9 degrees celcius – climate.nasa.gov
- Global average temperature (globally averaged near-surface air temperature) has risen by around 0.8°C between 1850 and 2012. – science.org.au
- Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade. – earthobservatory.nasa.gov
- 10 of the warmest years on record have occurred since 1990 – ucsusa.org
What Is The Significance Of The Current Rate Of Warming?
- While there have been past periods in Earth’s history when temperatures were warmer than they are now, the rate of change that is currently taking place is faster than most of the climate shifts that have occurred in the past, and therefore it will likely be more difficult to adapt to.
- Global climate has varied greatly throughout Earth’s history. In the final decades of the 20th century, the world experienced a rate of warming that is unprecedented for thousands of years, as far as we can tell from the available evidence [although Earth’s climate history goes back hundreds of millions of years].
How Warm Did Climates & Earth Temperatures Get In The Past Throughout Earth’s History?
There’s probably two main ways to look at the temperatures and climate conditions in the earth’s history:
- The last 22,000 years or so since 20,000BC – the earth was in an ice age in 20,000BC at -4.3 degrees celcius. Slight changes in Earth’s orbit at around 18500 BCE meant some of that polar ice could finally be reached by more sunlight, and the warming period began. Warming was gradual, with some periods of temporary cooling, until we hit the 20th century when warming increased rapidly [and we reach the point we are at today] – this coincides with significantly higher greenhouse gas emissions from humans.
- The record of the distant past (millions of years) tells us that climate has varied greatly through Earth’s history. It has, for example, gone through ten major ice age cycles over approximately the past million years. Over the last few thousand years of this period, during which civilisations developed, climate was unusually stable.
- 20,000BC and the different periods prior to that (up to hundreds of millions and billions of years) – prior to 20,000BC, earth’s climate varied more throughout different periods of time. The last 3 million years have been characterized by cycles of glacials (colder periods) and interglacials (warmer periods) within a gradually deepening ice age. A more extended ice age began about 40 million years ago (that eventually fed into the peak of the ice age at 20,000BC). 40 million years + ago, it is thought earth’s climate could fluctuate heavily, and there were several abrupt climate events and periods of very high temperatures throughout different periods. It’s worth noting that ancient climate change is interpreted through ancient earth records like ice cores and rock sediment samples, and interpretations can be more of an educated guess than an absolute certainty the further we go back.
You can check out and infographic, and also a timeline plot graph of Earth’s average temperature at:
Some of the warmest period’s in earth’s history to note are:
- About 65 million years ago – During the PETM [period], the global mean temperature seems to have risen by as much as 5-8 °C (9-14 °F) to an average temperature as high as 23 °C (73 °F), in contrast to the global average temperature of today at just under 15 °C (60 °F).
- About 66 to 100 million years ago – During the later portion of the Cretaceous … average global temperatures reached their highest level during the last ~200 million years.
- About 100 million to 542 million years ago – a period of fluctuating temperature between ice ages, such as the current age, and “climate optima”, similar to what occurred in the Cretaceous. Roughly 4 such cycles have occurred during this time with an approximately 140 million year separation between climate optima.
- There were also abrupt climate change events which usually involved a quick rate of warming or cooling…
- Past events include the end of the Carboniferous Rainforest Collapse, Younger Dryas, Dansgaard-Oeschger events, Heinrich events and possibly also the Paleocene–Eocene Thermal Maximum.
- Changes recorded in the climate of Greenland at the end of the Younger Dryas, as measured by ice-cores, imply a sudden warming of +10 °C (+18 °F) within a timescale of a few years. Other abrupt changes are the +4 °C (+7.2 °F) on Greenland 11,270 years ago or the abrupt +6 °C (11 °F) warming 22,000 years ago on Antarctica.