Global Climate Change Science Isn't Settled
by Jan Veizer
Many people think the science of climate change is settled. It isn't. And the issue is not whether there has been an overall warming during the past century. There has, although it was not uniform and none was observed during the past decade. The geologic record provides us with abundant evidence for such perpetual natural climate variability, from icecaps reaching almost to the equator to none at all, even at the poles.
The climate debate is, in reality, about a 1.6 watts per square metre or 0.5 per cent discrepancy in the poorly known planetary energy balance.
Let me explain. Without our atmosphere, the Earth would be a frozen ice ball. Natural greenhouse warming, due to atmospheric blanket, raises the temperature by about 33C. At least two-thirds of this warming is attributed to the greenhouse effect of water vapour.
Water vapour, not carbon dioxide, is by far the most important greenhouse gas. Yet the models treat the global water cycle as just being there, relegating it to a passive agent in the climate system. Energy that is required to drive the water cycle and generate more water vapour must therefore come from somewhere else: the sun, man-made greenhouse gases, other factors or any combination of the above.
Note, however, that because of the overwhelming importance of water vapour for the greenhouse effect, existing climate models are unlikely to yield a definitive answer about the role of carbon dioxide v the sun, for example, and the answer must be sought in past records.
The past climate record does indeed resemble the trend in solar output. However, because three decades of satellite data show only limited variability, the solar output would have to be somehow amplified to explain the entire magnitude of the centennial warming. The Intergovernmental Panel on Climate Change argues that because no amplifier is known, and because the atmospheric concentrations of carbon dioxide did increase from 280 parts per million to 370ppm, man-made greenhouse gases must be responsible for most of the energy imbalance.
But this is an assumption, an attribution by default, not an actual empirical or experimental proof that carbon dioxide is the driver. Yet such attribution is then taken as a fact in the subsequent complex model calibrations of climate sensitivity to CO2.
If, however, an amplifier to solar output does exist, and empirical observations detailed below argue for its existence, the need to attribute the energy input to man-made greenhouse gases would diminish accordingly. So how realistic is the basic model assumption that the tiny - biologically controlled - carbon cycle drives the climate via the passively responding huge water cycle?
Nature tells us that it is the other way around. Surely, the blossoming of plants in the spring is the outcome, not the cause, of the warming sun and abundant rain.
Our atmosphere contains 730 billion tons of carbon as CO2. Each year about 120billion tonnes of carbon are cycled via plants on land and 90billion tonnes via oceans. Human emissions account for about seven billion to 10billion tonnes, or less than 5 per cent, of the annual CO2 flux.
From the point of view of interaction of the water and carbon cycles it is important to realise that for every unit of CO2 sequestered by a plant from the atmosphere almost 1000 units of water must be lifted from the roots to the leaf canopy and eventually evaporated back into the air.
The required huge energy source is the sun. Solar energy drives the water cycle, generating a warmer and wetter climate while invigorating the biological carbon cycle. The sun also warms the oceans that emit their CO2.
Atmospheric CO2 is thus the product and not the cause of the climate, as demonstrated by past records where temperature changes precede changes in atmospheric CO2 concentrations and fluxes: ice cores, the 1991 Mt Pinatubo volcanic eruption in the Philippines or seasonal oscillations are instructive examples.
But what might be the complementary source of energy that could account for the disputed 1.6W/m2?
Clouds are a mirror that reflects solar radiation back into space. The amount of solar energy reflected by the Earth is about 77W/m2 and the difference between cloudless and cloudy skies is about 28W/m2. Therefore a change of just a few per cent in cloudiness easily can account for the disputed energy discrepancy.
Clouds are an integral part of the sun-driven water cycle; however, formation of water droplets requires seeding and this is where solar amplification likely comes into play. Empirical and experimental results suggest that cosmic rays hitting the atmosphere may generate such initial seeds, particularly over the oceans. While the actual mechanisms are still debated, the correlations between cloudiness and cosmic ray flux already have been published.
The amplifying connection to the sun comes via its electromagnetic envelope, called the heliosphere, and a similar envelope around the Earth, the magnetosphere. These act as shields that screen the lethal cosmic rays from reaching our planet. A less active sun is not only colder but its heliospheric envelope shrinks, allowing more cosmic rays to reach our atmosphere and seed more clouds, and vice versa. Indeed, satellite data for the past decade shows a 25per cent shrinking of the heliosphere that is coincident with the halt, or even decline, in planetary temperature since 1998: a trend at odds with the ever rising levels of atmospheric carbon dioxide.
We also have direct evidence for the above scenario. Cosmic rays, when hitting the atmosphere, generate a cascade of cosmogenic nuclides that then rain down to the Earth's surface and can be measured in ice, trees, rocks and minerals. Such records over the past 10,000 years correlate well with the highly variable climate, while the contemporary concentrations of CO2, measured in ice cores, are flat around the low pre-industrial levels of 280ppm with no resemblance to climate trends.
These centennial to millennial correlations, coupled with direct observations of coincidence of cloudiness with cosmic rays and temperature in central Europe since 1978, argue that the sun and its amplifying mechanism must play a leading role in climate control even if the cosmic ray signal proves no more than an indirect measure of solar variability.
The science of climate change continues to evolve and regardless of the outcome of the climate debate, observational data suggests that we may be served well by basing our climate agenda, scientifically and economically, on a broader perspective than that in the IPCC outlined scenarios. Our pollution abatement and energy diversification goals could then be formulated, and likely implemented, with less pain.
Jan Veizer is a distinguished university professor of geology (emeritus) at the University of Ottawa and has researched the use of chemical and isotopic techniques in determining Earth's climatic history.