What are climate change records?
There are many different ways in which data from climate has been recorded. In the modern past it has been with the use of satellites and advanced weather stations taking data from the atmosphere in balloons, or from below the surface of the ocean. The provide world-wide coverage. Going further back in the last century the data was recorded in weather stations that provided limited geographical coverage. If we go back more than 100 years there are very few, isolated records. Beyond a couple of hundred years ago the data record collected by people starts to peter out. We therefore need to turn to proxy records. These come from a wealth of sources. From the studies of tree rings, ice cores, coral reefs and sediment layers, to name some of the main ones. Data collected from these are not as accurate as data collected directly.
However, when the results are overlapped and compared a record of the climate in Earth’s past and how it has changed emerges, from 100’s of years (tree-rings) to hundreds of 100’s (ice cores) to millions (sediment layers) before present.
How do volcanoes affect climate change?
The constant shifting of the Earth’s tectonic plates produces volcanic eruptions in some parts of the world. When these occur vast clouds of ash are emitted into the atmosphere, along with other aerosols. One case study is that of the eruption of the Laki fissure system in 1784. Benjamin Franklin recorded that the following months were much cooler than expected across Europe and inferred that the volcanic eruption could be the cause. Records show that temperature across the Northern Hemisphere that year dropped by about 1 degree, which had severe impacts across the area in the form of food shortages and famine. So how did this eruption cause such a dramatic cooling effect? The aerosols and gasses emitted from the eruption form sulphates in the atmosphere. Sulphate aerosols can settle high in the atmosphere and remain there for months or even years. These aerosols are considered ‘light’ which means that they have a high albedo level and are very effective at reflecting radiation from the sun back into space, cooling the surface below. A good diagram of the overall interactions and effects of a volcanic eruption can be found in the paper “Volcanic eruptions and climate” by Alan Robock. See below, or HERE for a link to the full article.
Refs:
http://www.aos.wisc.edu/~aos915/Robock_2000.pdf
http://www.scientificamerican.com/article/how-do-volcanoes-affect-w/
http://www.cru.uea.ac.uk/documents/421974/1295957/Info+sheet+%2313.pdf/8f7e9115-8a35-4ec2-b45d-f3ba36524a44
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