Case for climate change

The origin and consequences of climate change

The widening gulf between scientific observations around the globe and public perceptions of the nature and origin of climate change is threatening to lead the world away from evidence-based policies despite projections by the world’s major climate research bodies (NASA/Goddard Institute of Space Science, National Snow and Ice Data Centre [Colorado], Hadley-Met, Tyndall Centre for Climate Change, British Antarctic Survey, Potsdam Institute for Climate Impact Research) as summarized in references[1], including the Australian Antarctic Division, CSIRO and Bureau of Meteorology[2]. A joint statement by the world’s academies of science states[3], among other: 

“However, climate change is happening even faster than previously estimated; global CO2 emissions since 2000 have been higher than even the highest predictions, Arctic sea ice has been melting at rates much faster than predicted, and the rise in the sea level has become more rapid. Feedbacks in the climate system might lead to much more rapid climate changes.” 

Below I refer to principal changes in the atmosphere/ocean/cryosphere system since the mid-20^th century. I avoid terms such as ‘denial’, ‘alarmist’ or ‘skeptic’. Skepticism is inbuilt into peer-reviewed science and is in no way an exclusive precinct of critics. As is the case with the medical profession, where evidence emerges for a danger to society raising a warning is the duty of scientists. Conspiracy theories can cut both ways and only serve to distract from the direct empirical evidence consistent with the laws of physics and chemistry. Nothing would relieve me and my colleagues more than if we were proven to be mistaken, if global warming would subside or, in the very least, could be shown to be a natural rather than a human-induced phenomenon. On the other hand I doubt if those who disagree with the evidence and the implications of climate change would wish to be mistaken. The consequences of such mistakes for humanity and nature would be severe.  

Dating back to Arrhenius (1896), Calendar (1938), Keeling (1960s) and the formulation of the laws of thermodynamics (Stefan-Boltzmann and Kirchoff’s laws), the infrared absorption/emission resonance effect of greenhouse molecules (water vapor, CO2, methane, ozone, nitric oxide) and recorded CO2-temperature relationships through time have become established tenets of atmospheric science. The global dispersal, cumulative nature and centuries to millennia-long residence time of atmospheric CO2 are contrasted with the more regional and transient nature of water vapor, with 9 days-long atmospheric residence time. Vapor concentrations are low over deserts and very low over the polar regions, yet it is the latter which are warming at a rate 3 to 4 times faster than the tropics (Figure 1 below).

The distinction between greenhouse, interglacial and glacial climate states (Figure 2) is related to the presence and extent of the polar ice sheets and of surrounding oceans, from where moist air vortices and cold currents emanate (Humboldt, California, West Africa). Warming of the poles weakens cross-latitude gradients, ocean currents and the wind vortices, extending the El-Nino mode and limiting the La Nina mode of the ENSO cycle, which ensues in droughts. Recent studies by NASA and the British Antarctic Survey[4] observe reduction of some 10 meters of ice per year since 2003. The thermal expansion of water and the consequence of continental ice melt are reflected by sea level changes which, since the early 20^th century to the present, rose from approximately 1 mm/year to 3.5 mm/year. Estimates of future sea level rise through the 21^st century, ranging between 0.6 and 5 meters, assume linear to accelerating warming trends. If abrupt temperature and sea level changes during the last glacial termination (about 20 – 10 thousand years ago) are any indication, fast changes are possible where climate tipping points are reached [5]. 

Much can be learnt from warm stages in the history of the atmosphere. Studies of Greenland and Antarctic ice cores and of marine sediments, using a range of proxies (including oxygen, carbon and boron isotopes, fossil plants, organic matter) identify close relations between the greenhouse gas concentrations and climate states (Figure 2). Current climate change, superposed on the Holocene interglacial, is distinct from the glacial terminations recorded in ice cores for the last 800 thousand years. Whereas the glacial terminations were initiated by solar radiation peaks, triggering rapid ice melt amplified by the (so-called) albedo flip effect (due to the contrast between high reflection by ice and strong absorption by water), warming of the oceans and release of CO2 lagged behind temperature rise by about 800 years[6]. 

The emission of more than 370 billion ton of carbon (GtC) since about 1750, more than 50 percent the original atmospheric inventory of 590 GtC, has pushed atmospheric CO2 levels from the interglacial maximum of about 280-300 parts per million (ppm) of the last 1.8 million years to the current level of 389 ppm, or 460 ppm when combined with the effect of methane, tracking toward the upper stability limit of 500 ppm CO2 of the Antarctic ice sheet[7] (Figure 2). Just under 50 percent of CO2 stays in the atmosphere (Figure 3). The current rate of CO2 rise of 2 ppm per year is almost unprecedented in geological record, barring the effects of major volcanic activity or asteroid impacts, which led to CO2-rich atmosphere and mass extinction of species. 

Lost too often in the climate debate is an appreciation of the delicate balance between the physical and chemical state of the Earth system and the evolving biosphere, which controls the emergence, survival and demise of species, including humans. Forming a thin breathable veneer only slightly more than one thousandth the diameter of Earth and evolving both gradually as well as through major perturbations, the atmosphere acts as a lung of the biosphere, allowing an exchange of carbon gases and oxygen with plants and animals, with feedbacks including release of methane. Species are capable of adapting to gradual environmental change, however, as testified by the geological record abrupt rises in CO₂, methane or H2S, injection of aerosol and dust, acidification of the oceans and consequent anoxia have led to the demise of species[8].  

Since the mid-20^th century climate patterns have been tracking toward conditions increasingly similar to those recorded for the mid-Pliocene, about 3 million years ago, a perspective which led the US Geological Survey to undertake extensive studies of Pliocene sediments. During the mid-Pliocene, with CO2 levels of 365-415 ppm and temperatures 3 to 4 degrees warmer that pre-industrial levels, large parts of the Greenland and Antarctic ice sheets melted, sea levels rose by about 25±12 meters and climate zones shifted toward the poles. Given the current rate of CO2 rise, future release of methane from permafrost, bogs and shallow sediments may reach levels similar to the Paleocene-Eocene Thermal Maximum (PETM) 55 million years-ago. At this stage release of c.2000 GtC as methane resulted in global temperature rise near-5 degrees Celsius. In this regard, the scale of global fossil fuel reserves, about 6000 GtC counsels caution. 

Claims as if high CO2 concentrations are beneficial for plants pertain to glasshouse conditions, where high humidity is maintained, but not to open agriculture where rising CO2 and thereby temperatures lead to droughts. Excess CO2 reduces the ability of respiratory pigments to oxygenate tissues and causes hypercapnia. The parts-per-million scale of CO2 concentrations should not conceal the danger posed by excess amounts of the gas, as is the case with the toxic effects of minute quantities of a variety of substances (cf. mercury, cyanide, arsenic). In marine environments, acidification due to excess CO2 and declining pH to below 8.2 results in production of bicarbonate and carbonic acid, which benthic fauna and corals can not use for shell growth.

Finally I comment on recent allegations against climate scientists and the IPCC. That a CRU climate scientist discusses the significance of a proxy-based temperature from tree rings[9] hardly amounts to a ‘climategate’ conspiracy” on the part of the scientific community. That the IPCC cites an uncertain projection for Himalayan glaciers melt (2035) does not indicate whether total Himalayan glaciers melt may occur earlier or later than this particular point in time. It must be stressed that, if anything, to date IPCC estimates of ice melt and sea level rise have been shown to constitute conservative underestimates which have already been exceeded[10].  No reason exists why people should trust climate scientists less than, for example, their medical doctors or air pilots.

At the roots of the climate debate is the precautionary principle. People insure their homes for small probabilities of loss. Nations build armed forces in connection with possible future contingencies. When faced with directly observed evidence of climate change, which led the premier science research bodies to warn the world of the consequences of the continuing emission of billions of tons of carbon, we better take note.

Consistent with the recent statement by Joachim Schellnhuber, Germany’s chief climate advisor: “We’re simply talking about the very life support system of this planet.”

Dr Andrew Glikson, Earth and paleo-climate scientist, Australian National University

Joanne Nova’s response to this essay, “No, Dr Glikson”, is here…

The two essays are being discussed at joannenova.com.au

Join the discussion here…

Figures:

Figure 1. Land (NASA/GISS) and ocean (NOAA) mean annual temperature anomalies for the period 2000-2009 relative to 1951-1980. Anomalies smoothed over 250 km. Note: (1) warming by up to 4 degrees Celsius over parts of the Arctic and west Antarctica; (2) warming of continental mid-latitude dry zones, including central Australia, by about 2 degrees C; (3) warming of large parts of ocean surfaces by up to 1.0 degrees C. Grey areas have no data. http://data.giss.nasa.gov/gistemp/maps/

Figure 2. Relations between atmospheric CO2 concentrations and glacial periods through time, showing the temporal distribution of ice ages and latitudinal extent of ice sheets. Note the correspondence between low CO2 levels below about 500 ppm CO2 and glaciations and between high CO2 levels and greenhouse climate states. ftp://rock.geosociety.org/pub/GSAToday/gt0403.pdf

Figure 3. Relation between the magnitude and proportions of the CO₂ cycle (in billion tons carbon per-year [GtC]) for the period 1850 – 2007, as related to fossil fuel emissions, deforestation, atmospheric accumulation and sequestration in the hydrosphere and land (vegetation and soil). Global Carbon Project http://unesdoc.unesco.org/images/0015/001500/150010e.pdf Note that, for the last decade, for emission of 7.5 GtC per-year and land clearing effects of 1.5 GtC per year, about 4.2 GtC remains in the atmosphere.