- CO2 (the most important gas) has risen from 280 parts per million (ppm) to slightly over 400 since pre-industrial times and its growth seems to be accelerating. Whether it does or not accelerate is the basis for 7 assumptions about future temperatures.
- Temperature increase. For the next 2 decades, 0.2 deg. C (0.4 F) temperature rise per decade, slightly higher later in most models. The models are all different and respond differently to different assumptions. For the end of this century, IPCC provides 7 best estimates (for 7 assumptions) ranging from 0.6 – 4.0 C (1.1-7.2 F). Warming is likely to lie in the range 2-4.5 deg. C (3.6-8.1 F), with a most likely value of about 3 deg. C (5.4 F). Since the 1800s the temperature has risen 0.76 deg.C (1.4 F). The warming is to be greater on land, in high northern latitudes. But let’s not forget that the temperature records start at the end of an unusually cold several centuries – the Little Ice age
- Sea level rise. For 6 sets of assumptions, the mid-points are about 0.3 meters ( 1 ft.) Since 1850 sea level has risen about 200 mm (9 in.), a little less than 2 mm/yr. More recently the rate appears to be 3.1 mm/yr, now measured by altimetry satellites. (However, we learned on 22 June 2007 that the data were manipulated to achieve this!!). A good explanation is by the late John Daly, whose passing was hailed by the IPCC ClimateGate scientists. In a 2009-published study, the authors used GPS measurement to correct for local vertical movement of the Earth at key tide gages, finding a “global rate of geocentric sea level rise of 1.61 ± 0.19mm/yr over the past century” and with no acceleration.
- Other attributes. Ocean acidity should rise with reduced ph units of 0.14 to 0.35; hurricanes become more intense, perhaps less numerous; heat waves and heavy precipitation more frequent; less sea ice and snow cover; higher westerly winds in mid-latitudes; more precipitation in high latitudes, less in sub-tropics inland areas.