Climate Change Explained
1. The global temperature has risen over the past century
1. The global temperature has risen over the past century
1. The global temperature has risen over the past century
Measurement of the global surface air temperature since 1880 shows an increase of about 1 degree Celsius. This finding is confirmed by all four major global temperature datasets (the University of East Anglia/Met Office, NASA, NOAA and the Japanese Meteorological Agency).
2. This follows a long period of prior stability
1. The global temperature has risen over the past century
1. The global temperature has risen over the past century
Reconstruction of the historic temperature record from tree rings and other proxies over the past thousand years shows a gentle decline across the centuries, through a "medieval warm period" at the start of the millennium and a "little ice age" mid-way. It is only in the last one hundred years that the pattern has changed and the global temperature has exhibited a sudden jump.
1. The global temperature has risen over the past century
3. Scientists have found the smoking gun: rising CO2
NOAA's Mauna Loa observatory
3. Scientists have found the smoking gun: rising CO2
3. Scientists have found the smoking gun: rising CO2
3. Scientists have found the smoking gun: rising CO2
Starting in 1958, the scientist Charles Keeling began recording the concentration of carbon dioxide in the atmosphere each year at NOAA's Mauna Loa Observatory in Hawaii. What he found was a surprise: a dramatic continuously rising trend. The level is now approaching 420 parts per million, from an initial base of 310 parts per million. Scientists believe that this increase is due to humankind's extraction and burning of fossil fuels (coal, oil and natural gas) for power, heating, industry and transportation since the industrial revolution.
They identify this rise as the cause of the observed leap in global air temperature. They locate the causal mechanism in a long-established physical property of carbon dioxide: its ability to absorb infrared radiation as heat. When infrared radiation is emitted by the Earth's surface after having been warmed by sunlight, it is absorbed by carbon dioxide molecules and trapped within the atmosphere as heat energy (the light passed unaffected through the atmosphere on its way in from the Sun because of its shorter wavelength). This is the known as the "greenhouse effect".
Adding to the planet's atmospheric concentration of carbon dioxide is analogous to a human being putting on additional layers of clothing.
3. Scientists have found the smoking gun: rising CO2
4. The link between CO2 and temperature is clear
Drilling ice cores
4. The link between CO2 and temperature is clear
3. Scientists have found the smoking gun: rising CO2
4. The link between CO2 and temperature is clear
Analysis of ice cores taken from the Antarctic and Greenland ice sheets reveals the historic concentration of carbon dioxide in the atmosphere (the gas is found in bubbles of ancient air trapped within the frozen ice). This record shows a remarkable and very close correlation with air temperature over the past 800,000 years, as the world has moved in and out of ice ages.
5. The current level of CO2 is nearly 50% above the prior stable level of the last 10,000 years
5. The current level of CO2 is nearly 50% above the prior stable level of the last 10,000 years
5. The current level of CO2 is nearly 50% above the prior stable level of the last 10,000 years
current level: 419ppm
broadly stable level of last 10,000 years: 280ppm
Given the close association with temperature, we would expect to witness significant warming.
The current level of carbon dioxide is also well outside the zone of familiarity of the last 800,000 years (170-300ppm).
6. The Earth is likely to continue heating up
5. The current level of CO2 is nearly 50% above the prior stable level of the last 10,000 years
5. The current level of CO2 is nearly 50% above the prior stable level of the last 10,000 years
Paleoclimatology, the reconstruction of Earth's past climate, indicates that it has experienced much hotter temperatures in the distant past (by up to 16 degrees Celsius). Scientists see carbon dioxide as the likely culprit for the historic instability over time, in what is termed the "carbon cycle". This is the process where the gas is successively drawn out of the atmosphere and deposited in rocks (known as weathering), leading to global cooling; and, in reverse, where the gas is released back out into the atmosphere with the ejection of magma from the Earth's core (known as volcanic venting), leading to global heating. The planet presently appears to have entered a rapid human-induced ejection phase, where the gas is artificially released from hydrocarbon fossil deposits buried underground. If this continues, it could end up considerably warmer than it is now.
7. We risk reaching a tipping point leading to runaway warming and a "hothouse Earth"
5. The current level of CO2 is nearly 50% above the prior stable level of the last 10,000 years
7. We risk reaching a tipping point leading to runaway warming and a "hothouse Earth"
Unless humankind takes action to curb its emissions of carbon dioxide (and other greenhouse gases such as methane and nitrous oxide), it risks an instance of "abrupt climate change", like those we have recently learned have happened in the past. Possible feed-back loops accelerating and accentuating the warming are phenomena such as: the melting of Arctic sea-ice reducing the reflection of sunlight (a lower "albedo" effect), leading to more absorption of light energy by the darker coloured oceans as heat, in turn causing further warming and ice loss; and the melting of permafrost in the Siberian and Canadian tundra or in ocean sediments, leading to the release of frozen methane deposits, in turn generating an intensified greenhouse effect. Scientists are concerned that triggering one or more of these feed-back loops could set off a chain of falling dominoes, passing a tipping point from the current benign equilibrium to a much less hospitable new equilibrium state: "hothouse Earth". This could prove unlivable for future generations.
8. What we have to do
8. What we have to do
7. We risk reaching a tipping point leading to runaway warming and a "hothouse Earth"
In order to begin putting things right and restore the broadly stable climate that our forefathers knew for future generations, we first need to stop emitting carbon dioxide: to reach "net zero" emissions. However, since the gas is long-lived in the atmosphere, with a duration of around 80 years, this will not be the end of the problem. Rather, it will be the point of maximum atmospheric concentration (a level of at least 600 parts per million is anticipated), and global temperature rise is expected to continue, if at a now declining rate. We will then need to remove carbon dioxide from the atmosphere, in a process known as "negative emissions", in order to return the concentration back to its original stable level of around 280 parts per million. Only then will the threat to life on planet Earth finally be over.