Some aspects of climate change have gone unchanged
According to the IPCC, although a number of changes have been documented, there are some aspects of the climate system that have not been observed to change thus far. Although Antarctic (South Pole) sea ice extent shows interannual variability and some localized changes, there are no statistically significant average trends to report at this time. The lack of change in the Antarctic is consistent with the lack of warming observed in atmospheric temperatures across the region.
Some believe that as temperatures continue to rise, climate change will result in more intense and more frequent thunderstorms and other severe weather events. While there is mounting evidence that global warming is contributing to more intense hurricane activity (presumably due to increased ocean surface water temperatures), to date there is insufficient evidence to determine whether trends exist in small-scale phenomena such as tornadoes, hail, lightning, and dust storms.
Natural variability versus human-induced change
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There is no doubt that Earth’s climate has naturally fluctuated throughout time, mostly because of naturally occurring processes processes. For example, ice core data indicate that polar temperatures were 3oC to 5oC higher than present during the last interglacial period (about 125,000 years ago), because of differences in the Earth’s orbit. As a result of melting polar ice, global average sea level during the last interglacial period was likely 4 to 6 m higher than present.
Climate changes and temperature variability over the last seven centuries, prior to 1950, can be attributed to volcanic eruptions, changes in solar irradiance, and other natural variations in the climate system. But have humans actually caused recent global warming? The answer is simple—yes.
According to the Intergovernmental Panel on Climate Change (IPCC), it is likely that human activities contributed to the warming evident in the early 1900s. Moreover, there is greater than a 90% chance that most of the observed increase in global average temperatures since the mid-20th century is due to the observed increase in anthropogenic greenhouse gas emissions.
Widespread warming of the atmosphere and the oceans, coupled with ice mass loss, are telling evidence of climate change. As the IPCC states, these observations “support the conclusion that global climate change of the past 50 years is very likely not due to known natural causes alone.” In fact, evidence points to significant anthropogenic warming averaged over each continent over the past 50 years, except Antarctica.
Moreover, the extent of global warming seen thus far could have been worse because volcanic and anthropogenic aerosols have helped to offset some warming by reflecting solar radiation back into space.