wildsage
earthling
(I wasn't ignoring you, just been busy.) I'm sure that you know the difference between "weather" and "climate." The idea behind the work of the IPCC was to avoid the worst-case scenario -- I know that for free-marketeers "worst case" means slowing consumption of limited resources -- which is increased global warming to the point where it threatens people, other species and our ability to maintain our societies & lifestyles.Yet, what is "short term"? Globally, regarding temperature? 1 year? 100 years? 1,000 years?
Show me long term, geologically speaking, man made global warming.
The ideal experiment when you don't have a large sample of subjects is non-destructive; it's a bad idea to sit back and say "yep, devastating, just like I thought." We only have the one planet so investigators rely on climate models to predict likelihoods of what may happen. They also test their models with historical data, some of it geologic in scale and some of it (more accurate) from recent history when information is better quantified.
Short term & long term are kind of subjective. The variables being studied to prove or disprove AGW of course focus on the rise of average global temps since the Industrial Age. (Short or long term? Your call.) These data are compared with paleological information with various other factors accounted for ("controlled") so as to isolate the phenomenon of interest. (Definitely long term, not much anthropogenic effect.) Current weather events -- whether last week or last month -- would likely be called short term.
From the IPCC:
"Although natural internal climate processes, such as El Niño, can cause variations in global mean temperature for relatively short periods, analysis indicates that a large portion is due to external factors. Brief periods of global cooling have followed major volcanic eruptions, such as Mt. Pinatubo in 1991. In the early part of the 20th century, global average temperature rose, during which time greenhouse gas concentrations started to rise, solar output was probably increasing and there was little volcanic activity. During the 1950s and 1960s, average global temperatures levelled off, as increases in aerosols from fossil fuels and other sources cooled the planet. The eruption of Mt. Agung in 1963 also put large quantities of reflective dust into the upper atmosphere. The rapid warming observed since the 1970s has occurred in a period when the increase in greenhouse gases has dominated over all other factors.
Numerous experiments have been conducted using climate models to determine the likely causes of the 20th-century climate change. These experiments indicate that models cannot reproduce the rapid warming observed in recent decades when they only take into account variations in solar output and volcanic activity. However [...] models are able to simulate the observed 20th-century changes in temperature when they include all of the most important external factors, including human influences from sources such as greenhouse gases and natural external factors. The model-estimated responses to these external factors are detectable in the 20th-century climate globally and in each individual continent except Antarctica, where there are insufficient observations. The human influence on climate very likely dominates over all other causes of change in global average surface temperature during the past half century."