I saw two interesting statements on climate change from the USA today. The first one is brand new, an update of the American Meteorological Society’s information statement on climate change, “based on the peer-reviewed scientific literature and … consistent with the vast weight of current scientific understanding”. I excerpt some of the highlights below, adding some headlines and comments.
Earth Is Warming
Warming of the climate system now is unequivocal, according to many different kinds of evidence.
Notably, among countless others this was also the result of a study funded by the Koch brothers who have made their fortunes from oil.
Surface temperature data for Earth as a whole, including readings over both land and ocean, show an increase of about 0.8°C (1.4°F) over the period 1901─2010 and about 0.5°C (0.9°F) over the period 1979–2010 (the era for which satellite-based temperature data are routinely available). Due to natural variability, not every year is warmer than the preceding year globally.
See here for a cute video illustrating the difference between long-term and short-term trends.
Nevertheless, all of the 10 warmest years in the global temperature records up to 2011 have occurred since 1997, with 2005 and 2010 being the warmest two years in more than a century of global records. (…)
The effects of this warming are especially evident in the planet’s polar regions. Arctic sea ice extent and volume have been decreasing for the past several decades. Both the Greenland and Antarctic ice sheets have lost significant amounts of ice. Most of the world’s glaciers are in retreat. (…)
In fact, Artic sea ice reached a new record low just a few days ago – with several more weeks of melting to go.
Globally averaged sea level has risen by about 17 cm (7 inches) in the 20th century, with the rise accelerating since the early 1990s. Close to half of the sea level rise observed since the 1970s has been caused by water expansion due to increases in ocean temperatures. Sea level is also rising due to melting from continental glaciers and from ice sheets on both Greenland and Antarctica.
Causes of Warming – It’s Us, Stupid
Climate is always changing. However, many of the observed changes noted above are beyond what can be explained by the natural variability of the climate. It is clear from extensive scientific evidence that the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO2), chlorofluorocarbons, methane, and nitrous oxide. The most important of these over the long term is CO2, whose concentration in the atmosphere is rising principally as a result of fossil-fuel combustion and deforestation. (…) Since long-term measurements began in the 1950s, the atmospheric CO2 concentration has been increasing at a rate much faster than at any time in the last 800,000 years. Having been introduced into the atmosphere it will take a thousand years for the majority of the added atmospheric CO2 to be removed by natural processes, and some will remain for thousands of subsequent years.
Again, even said Koch-funded study was forced to admit that essentially all of the global temperature increase has been caused by human emissions of greenhouse gases.
And by the way, the fact that much of the CO2 we emit will stay in the atmosphere for thousands of years means that it is nonsense to think that we can buy time by first tackling other less difficult greenhouse gases.
We Can’t Even Forecast Tomorrow’s Weather Properly, So How Are We Supposed to Forecast What Will Happen in 50 Years?
The difference between weather and climate is critically important in considering predictability. Climate is potentially predictable for much longer time scales than weather for several reasons. One reason is that climate can be meaningfully characterized by seasonal-to-decadal averages and other statistical measures, and the averaged weather is more predictable than individual weather events. A helpful analogy in this regard is that population averages of human mortality are predictable while life spans of individuals are not. A second reason is that climate involves physical systems and processes with long time scales, including the oceans and snow and ice, while weather largely involves atmospheric phenomena (e.g., thunderstorms, intense snow storms) with short time scales. A third reason is that climate can be affected by slowly changing factors such as human-induced changes in the chemical composition of the atmosphere, which alter the natural greenhouse effect. (…)
Because it would take many years for observations to verify whether a future climate projection is correct, researchers establish confidence in these projections by using historical and paleoclimate evidence and through careful study of observations of the causal chain between energy flow changes and climate-pattern responses. A valuable demonstration of the validity of current climate models is that when they include all known natural and human-induced factors that influence the global atmosphere on a large scale, the models reproduce many important aspects of observed changes of the 20th-century climate, including (1) global, continental, and subcontinental mean and extreme temperatures, (2) Arctic sea ice extent, (3) the latitudinal distribution of precipitation, and (4) extreme precipitation frequency.
In fact, climate scientists have actually demonstrated predictive power as well. For instance, the renowned NASA scientist James Hansen in 1981 quite accurately predicted the global temperature increase we have seen in the three decades since.
Future Impacts of Climate Change
In the 21st century, global sea level also will continue to rise although the rise will not be uniform at all locations. With its large mass and high capacity for heat storage, the ocean will continue to slowly warm and thus thermally expand for several centuries. Model simulations project about 27 cm (10 inches) to 71 cm (28 inches) of global sea level rise due to thermal expansion and melting of ice in the 21st century. Moreover, paleoclimatic observations and ice-sheet modeling indicate that melting of the Greenland and the West Antarctic ice sheets will eventually cause global sea level to rise several additional meters by 2500 if warming continues at its present rate beyond the 21st century. (…)
Climate-model simulations further project that heavy precipitation events will continue to become more intense and frequent, leading to increased precipitation totals from the strongest storms. This projection has important implications for water-resource management and flood control. The simulations also indicate the likelihood of longer dry spells between precipitation events in the subtropics and lower-middle latitudes, with shorter dry spells projected for higher latitudes where mean precipitation is expected to increase. (…)
Widespread retreat of mountain glaciers is expected to eventually lead to reduced dry season flows for glacier-fed rivers. Drought is projected to increase over Africa, Europe, and much of the North American continental interior, and particularly the southwest United States.
Which is right now suffering a drought of historic proportions, getting a taste of what climate change going to mean for them.
Enter Paul Ryan
With this as background, one can but cringe when reading this op-ed by Paul Ryan, newly anointed Republican Vice-Presidential candidate. It several years old but still featured on his website. Climate scientist Raymond T. Pierrehumbert dissects it expertly, here’s an appetiser:
He starts off with a cheap shot by implying that Wisconsin residents ought to have a hard time believing that global warming is a problem because they still had to shovel snow in the winter of 2009. Of course, it is absurd to think that any one winter says anything about global warming, still less to think that continued existence or even increase of snowfall is in any way incompatible with overall warming. If Ryan wanted to keep things local, he would have done better to talk to ice fishermen on the Wisconsin lakes, who have seen a dramatic decrease in the duration of ice cover over the past decades.
In this op-ed, Ryan reveals a number of still more alarming beliefs, notably that emails stolen from the East Anglia Climate Research Unit (aka Climategate) show that “leading climatologists make clear efforts to use statistical tricks to distort their findings and intentionally mislead the public on the issue of climate change,” and reveal “a perversion of the scientific method, where data were manipulated to support a predetermined conclusion.” He even claims that “The e-mail scandal has … forced the resignation of a number of discredited scientists” which is not at all true. (One scientist, Phil Jones, temporarily stepped aside while an investigation was taking place.) In fact, the hack was a manufactured controversy, and the real victims were the scientists whose emails were stolen. All have been exonerated completely by numerous independent panels, to say nothing of the fact that the key finding of the Climate Research Unit regarding the global temperature increase has been independently reproduced by the project of now-former-skeptic Richard Muller, who even received Koch funding for his study.
Elsewhere, Ryan wrote that “there is growing disagreement among scientists about climate change and its causes,” which is manifestly not true (see here and here) at least in the reality-based community where one counts only those with real scientific credentials and a track record of having done serious research in the subject.