IPCC Fifth Assessment Report on Climate Change: Global Warming Attributable to Human Influence

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Huma enrgy consumption from fossil fuels contributes to atmospheric carbon dioxide levels. Photo by BenutzerPriwo

Huma enrgy consumption from fossil fuels contributes to atmospheric carbon dioxide levels. Photo by BenutzerPriwo

For example, the warming of the oceans has implications for the transport of heat around the planet. The loss of land and sea ice (as a result of atmospheric warming) is directly associated not just with the observed increase in sea level rise, with consequent implications for low-lying coastal regions, but also with changing the temperature and salinity of the oceans at high latitudes – also influencing ocean circulation, heat transport and regional climate.

And increased warming increases the amount of water vapour in the atmosphere – leading, scientists think, to intensification of the hydrological cycle with potential increase in strength of high-energy weather events such as storms and hurricanes.

The Fifth Assessment Report looks beyond the observed changes to the future, and their assessment is bleak.
• Researchers expect that warming will continue at least until 2100, although it will not be uniform.
• Changes to the hydrological cycle won’t be uniform either, but it’s likely that wet regions and seasons will become increasingly wet and dry regions/seasons increasingly dry.
• Ocean warming will continue and will have an impact upon circulation.
• Sea level rise will continue.

Global Climate Change: Human Influence or Natural Variability?

The Earth’s climate shows natural variability on all cycles, from months to thousands of years, and scientific research shows that this variation has been occurring over millions of years.

We know that our current climate, even with present levels of change, is by no means the warmest it has been. Yet the IPCC is in no doubt about where the responsibility for current change lies: “Human influence on the climate system is clear. This is evident from the increasing greenhouse gas concentrations in the atmosphere, positive radiative forcing, observed warming, and understanding of the climate system.

How can they be so sure? Scientists can ‘read’ ancient atmospheric compositions from bubbles trapped in ice cores and from sediment cores. Carbon dioxide has many natural sources but a key one is the use of fossil fuels, the burning of which releases the gas.

Graphs of atmospheric carbon dioxide show a rapid increase after the middle of the nineteenth century – the point at which rapid industrialisation led to the use of coal, then oil and gas, to provide rapidly increasing amounts of energy for the world’s needs.

Man-Made Climate Change Controversy

Despite the findings of the IPCC and their assertion that change is increasing and that it’s humans who are responsible, the issue is not without controversy. In the past climate scientists have been criticised for publishing inaccurate and even deliberately misleading information; and even in the week that the IPCC released its report, new research suggests that the warming trend they report has stopped – although the scientists who published the research note that it is probably part of natural variability and that “the multi-decadal warming trend is very likely to continue with greenhouse gas increase.

The problem for climate researchers, and for the rest of us, is that scientists don’t fully understand the workings of the Earth system and its feedbacks can be negative (working against change) as well as positive. Human-induced changed has to be balanced against natural climate variability, which can be long-term and significant. Despite these caveats, the evidence suggests that we are indeed in a period of rapid atmospheric warming and that this will have major implications for the planet – and its human population.

Sources

IPCC. Climate Change 2013: The Physical Science Basis. Headline Statements from the Summary for Policymakers. (2013). Accessed September 27, 2013.

IPCC Press Release. Human influence on climate clear, IPCC report says. (2013). Accessed September 27, 2013.

Kosaka, Y and Xie, S-P. Recent global-warming hiatus tied to equatorial Pacific surface cooling. (2013). Nature. Accessed September 27, 2013.

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