Climate Science - A Brief History of our Climate

Our climate has always been changing, but understanding that history lets us see today’s changes in their full context. That context shows us the speed and extent of Climate Change really is as alarming as it seems.

In this blog, Part 4 of our Climate Science series, we will walk you through the history of our climate and show the key changes in temperature and concentration of CO2, what caused them and how fast the changes were. This context will help show just how dramatic the climate change we see today really is, and just how urgently action is required.

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What was our atmosphere like in the past?

4.5 billion years ago (bya) – 500 million years ago (mya)

Since forming 4.5 billion years ago the Earth’s atmosphere has gone through huge transformations, and three distinct types of atmospheres. The early atmosphere was a toxic mixture of Ammonia, Methane & Hydrogen, eventually tectonic activity and asteroid impacts led to Nitrogen becoming the dominant gas in a second atmosphere. It wasn’t until 2.4 billion years ago that Oxygen began to take up a larger share, forming the third atmosphere.

As the atmosphere changed so did the planet itself. The first two periods of widespread glaciation, known as Ice Ages, were caused by a combination of plate tectonic activity and Earth’s orbit shifting, the first roughly over 2 bya and another just over 600 mya.

The early changes to our planet were certainly dramatic, but its worth remembering that they took place over very long timescales, and so actually happened incredibly slowly.

500 mya- 1 mya

Up until about 50 million years ago there were huge shifts in CO2 levels, peaking at 6,000ppm (parts per million) and dropping to around 400ppm. From 50 mya onwards CO2 declined steadily from 1000 ppm all the way to 200 ppm.

It is worth noting that the last time CO2 concentrations were 412ppm (todays value) was roughly 3 million years ago

[Figure 1] - CO2 ppm (parts per million) over time

Over the same period the temperature of the planet also varied wildly. Three more distinct ice ages occurred, with the third starting roughly 3 mya and continuing to this day (yes - thanks to our rapidly dwindling polar ice caps we are technically living in an ice age!).

[Figure 2]- Global Temperature Changes over time

800,000 years ago – 1700 AD

From 800,000 years ago, we start to get much more accurate data from ice cores. These are cylinders of ice drilled out from ice sheets or glaciers. The longest ice cores are up to 3km in depth, and trap bubbles from the atmosphere to give us a snapshot of the concentration of various gases at the time when the air was sealed in the ice.

To give some context, 800,000 years ago early apes like Homo Erectus were hunting and gathering but our own species, Homo Spaiens, had not yet evolved. “Humans” would not show up until 300,000 years ago.

During this period the CO2 and temperature both fluctuated, not as wildly as in the very early earth but there were significant variations, with CO2 following the temperature astonishingly closely. It is worth noting the CO2 levels never breached 300ppm.

[Figure 3] - CO2 vs Temp over the last 800,000 years

1700 AD - Present Day

Humans have had an impact on the climate since long before factories and cars began emitting greenhouse gases on a huge scale. We have changed the landscape through agricultural practises and deforestation, and have changed eco-systems through overfishing and over hunting.

But after the industrial revolution, and as the world’s population grew in the 20th century, the scale of humans impact on the atmosphere and the climate grew alarmingly. CO2 levels have skyrocketed, as Figure 4 shows. A new record for the last 800,000 years was broken around 1900 with a concentration of 300ppm, and it has only risen since.

[Figure 4] - CO2 Levels since 1700

As set out in our previous blog, from 1958 onwards we have a consistent record of CO2 levels in the atmosphere taken from the Mauna Loa observatory, forming the famous “Keeling Curve”. This shows a precipitous increase in CO2 concentrations, breaching 400ppm in 2016 and continuing to rise today. The increase is even more stark when you look at it over the longer timescale in Figure 4.

[Figure 5] - The Keeling Curve

Not only have the CO2 levels skyrocketed, but since 1880 the temperature has risen by 1degC. The warmest years on record have all occurred since 1998 and the impact of this warming is already being felt across the world.

The greenhouse effect is causing temperatures to rise along with the rising CO2 levels

[Figure 6] - Temperature increase since industrialisation

After a whistle-stop tour of the last 4.5 billion years of Earth’s climate what can we conclude?

Well, we know that “climate change” has always been occurring in one form or another, but the rapid rise in CO2 and temperatures that we are seeing now are actually a noticeable break from the fluctuations of the past. The changes we are seeing today are not as vast as those of the early planet, but they are happening much much faster, over decades not millennia. They are not insignificant changes either, CO2 levels are the highest they have been in millions of years, because of greenhouse gas emissions, and global temperatures are rising alarmingly fast.

We may technically be living in an ice age, but for how much longer?

Our next blog will look to the future, examine how scientists map out scenarios and model the Earth’s climate, and we examine what each scenario would mean for life as we know it.

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Figures & Citations:

[Figure 1]

FOSTER ET AL/DESCENT INTO THE ICEHOUSE

[Figure 2]

Palaeotemps - Glen Fergus

[Figure 3]

https://earthobservatory.nasa.gov/features/CarbonCycle/page4.php. Graphs by Robert Simmon, using data from Lüthi et al., 2008, and Jouzel et al., 2007.

[Figure 4]

https://sioweb.ucsd.edu/programs/keelingcurve/wp-content/plugins/sio-bluemoon/graphs/. https://doi.org/10.1029/2006GL026152. MacFarling Meure, C., D. Etheridge, C. Trudinger, P. Steele, R. Langenfelds, T. van Ommen, A. Smith, and J. Elkins. 2006. The Law Dome CO2, CH4 and N2O Ice Core Records Extended to 2000 years BP. Geophysical Research Letters, Vol. 33, No. 14, L14810 10.1029/2006GL026152.

[Figure 5]

http://scrippsco2.ucsd.edu/data/atmospheric_co2/primary_mlo_co2_record http://doi.org/10.6075/J08W3BHW. C. D. Keeling, S. C. Piper, R. B. Bacastow, M. Wahlen, T. P. Whorf, M. Heimann, and H. A. Meijer, Exchanges of atmospheric CO2 and 13CO2 with the terrestrial biosphere and oceans from 1978 to 2000. I. Global aspects, SIO Reference Series, No. 01-06, Scripps Institution of Oceanography, San Diego, 88 pages, 2001. http://escholarship.org/uc/item/09v319r9

[Figure 6]

https://data.giss.nasa.gov/gistemp/graphs_v4/ NASA Goddard Institute for Space Studies. Lenssen et al. (2019).