6 Session 2 summary
Very many aspects of the Earth system are changing, with important consequences for human and other life. Detecting climate change, and designing and testing geoengineering, requires long data records, over the whole globe, to measure how much climate has changed in the past and whether future geoengineering is working as expected.
Global mean surface temperature records show clear warming since 1850, though large interannual (year-to-year) variability makes the picture more complex. Local changes can be much larger than the global mean. The widespread changes provide motivation for reducing climate change and its risks, but also complicate the design of any geoengineering proposed.
Difficult decisions must be made about reducing one aspect of Earth system change over another, protecting one place over another, and reducing harm to one vulnerable aspect of life over another.
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