Satellites should answer the central question of climate

On January 3rd, the widely-respected Earth System Science Center at the University of Alabama at Huntsville (UAH) published its satellite-derived average temperature of the lower atmosphere for December 2010. It showed that the 13-month running average is roughly level with the 1998 figure (readings for both years were elevated by El Nino events). The running average reinforces the fact that, at least for the past 12 years, there’s been no global warming. Meanwhile, over those same 12 years, carbon dioxide in the air rose by 6%: so what’s going on? Either the warming influence of man-made CO₂ has been offset by some still unspecified cooling - or the man-made global warming theory must be questioned.

In October 2010, an interesting conference - the A-Train symposium - was held in New Orleans. It refers to the "afternoon train" of satellites - Aqua (launched in 2002), Aura (launched in 2004), CloudSat (launched in 2006) and CALIPSO (also launched in 2006) - that cross the equator at around 1:30 p.m. local time each afternoon, giving the formation its name. Together, these four satellites carry 15 instruments that survey an identical slice of Earth’s surface and atmosphere as they pass overhead. Leading the train, Aqua measures temperature, water vapour, and rainfall; then CloudSat and CALIPSO track clouds and aerosols; flying last, Aura logs greenhouse gases in the air.

Data from these satellites could answer a key question that should settle the climate debate: how much warmer would it really get - not just in theory - if CO₂ were doubled? In its 2007 Assessment Report, the Intergovernmental Panel on Climate Change handled this question of "climate sensitivity" (usually expressed in terms of deg.C/W/m²) with computer models. IPCC assumed that a theoretical temperature rise from CO₂ alone would be theoretically amplified by water vapour, in a "positive feedback", by a factor of between 2.0 and 4.5. It’s logical: if it gets warmer, there’ll be more surface evaporation, more water vapour in the air - and a warmer surface. But has it been proven that water vapour causes further warming? In fact, it hasn’t.

Nevertheless, all sides in the debate have much to agree on: that climate has always changed and always will; that the "greenhouse" keeps the Earth’s temperature about 34^oC warmer than it would otherwise be; that water vapour and clouds account for about 95% of greenhouse gases; that CO₂ is a minor greenhouse gas at 3.5% of all greenhouse gases and 0.039% of the air; that warming from a doubling of CO₂ by itself would, in theory, be perhaps 1°C; that since the Little Ice Age of around 1350 to 1850, it’s been getting warmer; that since around 1850, CO₂ in the air has been increasing and now stands at 390 parts per million; that CO₂ comes from many sources, natural and man-made; and that CO₂ from man-made sources accounts for 7 billion tonnes of the 220 billion tonnes of carbon equivalent emitted each year - or about 3%. But the question of whether man-made CO₂ causes unprecedented and dangerous global warming - the notion behind so much social and political angst about "carbon" - remains in serious dispute.

With observational data now becoming available from high-resolution instruments flown on specialised satellites, we could soon have a resolution to the key question of whether water vapour amplifies or attenuates temperature rises from CO₂ alone. Recent peer-reviewed research in leading journals suggests the assumption that water vapour feedback adds to temperature rises from more CO₂ - and leads to climate catastrophe - may simply be wrong. Among recent papers, two stand out.

In August 2009, Dr Richard Lindzen of MIT and his collaborator Dr. Yong-Sang Choi inferred from satellite data that feedback isn’t positive at all. Using observations from the ERBE instrument on the ERBS satellite (launched in 1984), they analysed the relationship between tropical sea-surface temperatures and top-of-atmosphere heat radiation - and concluded that feedback is far lower than the positive 2.0 to 4.5 times assumed in IPCC’s models and is in fact negative. The Lindzen-Choi results were attacked as flawed by Dr Kevin Trenberth, the IPCC scientist who, in the Climategate emails, noted himself that global warming has stopped. Responding positively to Trenberth’s comments, Lindzen and Choi analysed further data, from the CERES instrument on the Terra satellite (launched in 1999) - and got results that actually reinforced their original finding. They pegged climate sensitivity due to the water vapour effect at 0.7°C per doubling of CO₂, suggesting that higher temperature from more CO₂ alone would be inconsequential in terms of historical, seasonal and daily temperature ranges.

In August 2010, Dr Roy Spencer and Dr. William Braswell of UAH published a paper, also based on observational evidence, from CERES and the AMSR-E instrument on the newer Aqua satellite. Spencer and Braswell likewise demonstrated that real feedback falls far below the theoretical levels built into IPCC models and must be negative. They showed that changes in the reflectivity of clouds are causes of constant adjustment in temperature, rather than effects hitherto believed to be positive feedback. They concluded that the water vapour effect of a doubling of man-made CO₂ alone would raise average temperature by 0.6^oC - which means that any signal of higher temperatures from more CO₂ would effectively be lost in the noise.

If this foundational assumption - that water vapour amplifies a greenhouse-induced rise in temperature - turns out to be wrong, then the notion that man-made CO₂ is a source of catastrophe for mankind is also wrong. And if the man-made CO₂ scare is mistaken, as these results suggest, then natural drivers of climate are at work.

Meanwhile, urgent environmental issues threaten millions of people today but, tragically, aren’t given the priority they deserve - because so much focus is misplaced by so many on something so theoretical and long-term as man-made climate catastrophe. We should focus instead on real, urgent, life-threatening issues like preventable disease, lack of fresh water, degradation of the oceans, deforestation and species extinction, while we wait to see what real observational data - not just theory - tells us about the drivers of our changing climate.