Now – Here
Humans are affecting the Earths climate. The genomes of organisms can be changed in a controlled way. Humans’ relationship to natural selection has changed. Information technology is changing society all over the globe. Earth-like planets are discovered in habitable zones around their host stars.
Image: The climate is warming. NOAA Climate.gov | Emily Greenhalgh | Marcott et al, Science, 2013
Climate warming and the green house phenomenon
The temperature of Earth’s atmosphere has risen during the 1900’s by 0,6 – 0,9 oC. This does not sound like much, but a rise of even of a few degrees can have major effects on the ecosystems, the ocean level, climate and weather, and therefore, on the human society. For example at late Cretaceous the average temperature was only about 5 oC higher and Europe was mostly covered by sea. The scientists generally believe that the climate warming has been mostly caused by human production of different greenhouse gases. The carbon dioxide content of the atmosphere has indeed risen from the 280 ppm up to the current 400 ppm level, and it is likely to continue its rise, due to the use of fossil fuels, and the altered land use. In addition, the climate warming can be further increased by positive feed-back loops, like the release of the methane hydrates under warmer conditions.
Greenhouse gases like carbon dioxide, methane and water vapor increase the Earth temperature, because they are transparent for the incoming solar radiation, but they absorb and block a large part of the heat radiation rising from the Earth surface. This effect is absolutely necessary for the habitability of our planet: without this greenhouse effect the planet would be very cold, and essentially no liquid water could be detected on the surface. Thus, the greenhouse effect itself is not a problem, but rather, the problem is its fast increase.
In the history of our planet, there are several other examples of major climate changes caused by the alterations in the greenhouse gases in the atmosphere, such as the mass extinction in the end of Permian, or, the Huronian super-glaciation. The levels of the greenhouse gases were very high on the young planet, but the glaciations were still possible due to the lower radiation level of the young Sun. We can say that the climate of our planet alternates between the greenhouse and the icehouse states. For most of its history, the planet has been under greenhouse state with temperatures significantly higher, with no glaciations on the planet, and with about 100 meters higher ocean levels, as compared to the present time. The change from one state to the other has often occurred very rapidly, and caused massive extinctions. It is worthwhile to consider how we, as a civilized society, would survive such a change.