I refer to G. Bailey's letter ("Still a lot of doubts about climate change", December 17).
He wrote: "No one denies climate change; the climate changes all the time."
However, that definition of climate change cannot be described as its mainstream meaning with all its widely understood connotations, a meaning that is accepted by the overwhelming majority of climate scientists. As such, he takes a position antipodal to that of numerous people believing in, or working on various parts of, the "climate change regime" in which the term "climate change" has a standard definition which he denies.
People like Danish astrophysicist Henrik Svensmark, who believe that solar activity variations have large impacts on global temperature, are only partially correct because they conveniently ignore two scientific facts. First, solar activity variations have roughly an 11-year cycle (hence, short term) and, by themselves, are not a determinant of long-term global warming or cooling. Second, decreased solar cycle intensity, as is currently the case, reduces heating of the earth but by a small fraction of the long-term - and increasing - heating of it due to rising atmospheric concentrations of greenhouse gases such as carbon dioxide.
Atmospheric carbon dioxide is now pushing 400 parts per million and increasing. Its gain since 1800 has already caused a global temperature rise of 0.8 degrees Celsius. Its major human- caused sources are land-use changes and fossil fuel combustion. Its heat-trapping physics are well known. Satellite data has unequivocally shown that the earth has been re-radiating less energy back to space than the solar radiation it receives. This trapped heat is somewhere in the earth's system, causing whatever system it is in to warm up.
The earth's oceans are monitored by more than 3,000 Argo floats. These floats measure the oceans' temperature, salinity, and current from the surface down to a depth of two kilometres. Fifteen years of Argo data show that the upper 2,000 metres of oceans have been gaining heat at a rate faster than that due to solar cycle variability.
Satellite radar, photo, and gravity data has confirmed a global sea level rise and ice loss from Greenland, Antarctica, and glaciers. Sea levels rise because the oceans' waters are warming and expanding, and because ice sheets are warming and melting.
Persistent denials of the causative relationship between climate change and anthropogenic carbon dioxide are astounding.
Patrick C. Lui, Palo Alto, California, US