The heat-trapping nature of carbon dioxide (CO2) and other gases was first demonstrated in the mid-19th century by Irish natural historian John Tyndall, who recognised the Earth’s natural greenhouse effect and suggested that slight changes in the atmospheric composition could bring about climatic variations.
Towards the end of the 19th century, Swedish scientist Svante Arrhenius predicted that changes in the levels of CO2 in the atmosphere could substantially alter the Earth’s surface temperature through the greenhouse effect.
In the late 1950s, CO2 monitoring commenced in earnest, but with mixed results. It wasn’t until the late 1960s, with the help of the first computer model to simulate the entire planet’s climate, that the first linkage between CO2 and global warming was established.
Over the next couple of decades, drilling of ice cores in glaciers around the world showed that the Earth’s climate has responded to changes in greenhouse gas levels over time. Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks.
This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly ten times faster than the average rate of ice-age-recovery warming, according to the US’s National Research Council (NRC).
Greenhouse gases (GHGs) include not only CO2 but methane (CH4), nitrous oxide (N2O), ozone (O3), and fluorinated gases (halocarbons).
Since the beginning of the Industrial Revolution in the middle of the 18th century, human activity has produced more than a 40 percent increase in the atmospheric concentration of the main cause of climate change, CO2 — from 280 parts per million (ppm) in 1750 to over 400 ppm today. While methane is a more potent GHG, there is over 200 times more CO2 in the atmosphere: CO2 levels are 380 ppm, while methane levels are 1.75ppm.
In 1990, the Intergovernmental Panel on Climate Change produced the First Assessment Report, concluding that temperatures had risen by 0.3-0.6 degrees Celsius over the 20th century, that humanity’s emissions are adding to the atmosphere’s natural complement of greenhouse gases, and that the addition would be expected to result in warming.
By the start of this century, the impact of rising greenhouse gas levels was becoming all too apparent: global sea levels have risen by about 200 millimetres due to melting ice at the two poles; the Earth’s average surface temperature rose about 1.1 degrees Celsius since the late 19th century; and the number of record high temperature events has been increasing along with increasing numbers of intense rainfall events.
With these scientific advances have emerged well-funded politically-based bodies promoting opposition to climate science: one of the first being the Information Council on the Environment in 1991; and by the closing years of the decade the American Petroleum Institute with its 1998 Global Climate Science Communication Action Plan.
There are also many corporations that have turned climate change into a business opportunity through the development of cleantech products, or have seen that it is responsible to lobby for climate change targets, or to make investments to reduce their greenhouse gas emissions.