The current rate of greenhouse gas rise is unprecedented in Earth history, excepting global volcanic events and asteroid impacts. The rise of atmospheric energy levels since the 18th century by 3.2 Watt/m2, masked in part by aerosols, leads the climate to more than 2 degrees temperature rise and metres-scale sea level rise.
Inherent in IPCC climate change projections are continuous trends towards mean global temperatures of 1.8 to 3.6 degrees by 2100, depending on emission scenarios, as adopted in the Stern and Garnaut reports, giving an impression as if mitigation and/or adaptation can be undertaken at any economically or politically chosen time over the next several decades.
Unfortunately this is not the case.
Studies of the atmosphere-ocean-cryosphere (polar ice) system, based on evidence from ice cores, deep sea sediments, coral reefs, cave deposits and other proxies, demonstrate abrupt changes between climate states over periods as short as a few centuries, decades and even few years.
Central to such changes is the radiative forcing state of the atmosphere, namely the positive or negative balance between incoming energy flow (warming) and outgoing energy flow (cooling) associated with solar insolation, surface albedo, greenhouse gas levels (water vapour, CO2, methane, N2O, halocarbons, ozone) and aerosols (SO2, dust, sooth). Since the 18th century radiative forcing rose by near to 3.2 Watt/m2, predominantly due to emission of over 320 billion tonnes of carbon (GtC) and deforestation. Temperatures, ice melt and sea level rise lag behind radiative forcing by unspecified periods.
Interglacial periods (~410, 330, 240, 140 kyr) similar to the current Holocene (11.7 thousand years-ago [kyr] to the present) provide essential benchmarks for the behaviour of the atmosphere under rising radiative forcings (Figures 1 and 2).
Figure 1. CO2, methane, temperatures based on deep ocean measurements, calculated temperatures, greenhouse gas forcing, surface albedo and sea level changes over the past 800,000 years. From Hansen and Sato, 2011.
Figure 2. Past global temperatures relative to mean Holocene temperature, based on ocean core records, with temperature change amplified by factor 1.5 (relative to Vostok-based estimates). Red arrow in upper diagram indicates temperature rise since 1750 consistent with the rise in atmospheric energy levels at 1.7 Watt/m2, indicating a committed rise of +1.2oC, or ~ +2.4 o rise without aerosol masking effects.
Previous interglacial periods were up to 0.7 degrees warmer than the mean value of the Holocene (Figure 2). For example a temperature rise at the Eemian, ~140 kyr ago was associated with sea level rise of about 5-7 metres relative to the present, setting a minimum for future sea level rise under current climate conditions.
Based on the study of ice cores and deep sea sediments, shifts between glacial and interglacial climates during the last 800,000 years (800 kyr) typically involved atmospheric energy changes of ~6.5+/1.5 Watt/m2, which is translated to ~5.0+/-1.0 degrees (Figure 1). This defines a relation between temperature and atmosphere energy level of approximately 0.75 degree per 1 Watt/m2 (Hansen et al., 2008, 2011).
The 3.2 Watt/m2 rise since the 18th century, in the absence of SO2 aerosols, commits the climate to near 4 degrees rise, exceeding previous interglacial periods (Figure 1). Such atmospheric energy levels can be compared with conditions that existed in the early to mid Pliocene (5.3 – 2.6 million years ago; <400 ppm CO2; T ~ +2 to +4 degrees; sea level +25+/-12 metres higher than the Holocene) (Figure 2) and the mid-Miocene (~16 million years ago; <650 ppm CO2; ~4 degrees; sea level +40 metres relative to the Holocene).
The expression of climate change through a series of extreme weather events around the globe, including heat waves, increased evaporation and precipitation and intensifying cyclone cells, remains little understood by the public. Lenton et al. 2008 state: “Society may be lulled into a false sense of security by smooth projections of global change. Our synthesis of present knowledge suggests that a variety of tipping elements could reach their critical point within this century under anthropogenic climate change.” (Figure 3)
Figure 3. Map of potential tipping elements in the climate system, overlain on global population density. Subsystems indicated could exhibit threshold-type behaviour in response to anthropogenic climate forcing, where a small perturbation at a critical point qualitatively alters the future fate of the system (Lenton et al. 2008).
While the timing of tipping points can not be determined, such may be preceded by lulls, as indicated by Dakos et al., 2008 (Figure 4): “… we analyse eight ancient abrupt climate shifts and show that they were all preceded by a characteristic slowing down of the fluctuations starting well before the actual shift … our results imply independent empirical evidence for the idea that past abrupt shifts were associated with the passing of critical thresholds.”
Figure 4. Reconstructed time series of abrupt climate shifts in the past. The arrows mark the width of the moving window used to compute slowness. The smooth grey line through the time series is the Gaussian kernel function used to filter out slow trends. Dakos et al. 2008.
The amplifying feedback mechanism of polar ice melt is the so-called albedo-flip effect, where loss of reflection by melted ice is compounded by infrared absorption by open water, a process currently taking place in the Arctic Sea, as reported by Hansen et al: “… amplifying feedbacks make ice sheet disintegration necessarily highly non-linear. In a non-linear problem, the most relevant number for projecting sea level rise is the doubling time for the rate of mass loss. Hansen (2007) suggested that a 10-year doubling time was plausible, pointing out that such a doubling time from a base of 1 mm per year ice sheet contribution to sea level in the decade 2005-2015 would lead to a cumulative 5 m sea level rise by 2095.”
Satellite studies of Greenland and Antarctic ice melt rates by Velicogna, 2009 and Rignot and Velicogna, 2011, who indicate acceleration of Antarctic and Greenland ice melt rates, forming major contribution for sea level rise.
It is not generally realised that, through rising atmospheric CO2 levels since ~8000 years ago due to fires and deforestation, and rising methane since ~5000 years due to rice cultivation and animal husbandry, civilisation has subconsciously postponed climate cooling toward the next ice age by near-2.7 degrees. Judicious science-based injection of greenhouse gases into the atmosphere would have been able to prolong interglacial Holocene conditions, justifying the term “homo sapiens”.
Instead, since the mid-18th century, uncontrolled release of fossil carbon from hundreds of million years-old fossil biospheres at <2 ppm/year, a rate unprecedented in geologic history (barring major volcanism and asteroid impacts), is pushing mean global temperatures toward climate conditions of millions of years ago when tropical conditions dominated much of the Earth and large parts of the continents were covered by seas.
Dr Andrew Glikson, Earth and paleo-climate scientist at the ANU.
So, if I’m reading this article correctly and pushing past all the political rhetoric, deforestation of the planet’s atmospheric lungs combined with unlocking carbon previously captured by trees is swinging the planet’s climate patterns from a more predictable, softer land/plant dominated system to a less predicable, more extreme ocean/inanimate dominated system?
And the best political vision we’ve got involves dicking around with another tax, a tax on carbon?
Is anyone apart from the Greens and some of the Nordic nations prepared to acknowledge that man clearly has a symbiotic relationship with trees?
Wouldn’t planting trees, lots and lots more trees, be the straightest path back to a more salubrious climate? Wouldn’t the simpler infrastructure solution of engineering forests in already arid, unused areas within Australia and around the globe using underground water and similar be preferable to increasing the bureaucratic flab of our parasitic public service to enable another unnecessary tax?
And if our keen minded politicians need a more personal upside, think of all those real estate commissions and stamp duties to be had from converting our deserts to forests and then selling them off, a quarter acre at a time.
@BOXINGCANDLE Posted Tuesday, 5 April 2011 at 3:42 pm
No, you cannot possibly believe it would be easy or inexpensive to convert our arid nutrient-poor soils into thriving forests? Water and phosphate are two critical ingredients and both are in short supply and expensive. (Indeed there is a veritable panic on about future phosphate supplies on which our modern agriculture has become totally dependent, so forget the ag lobby sitting by watching it being used for forests.) So it is where natural equitorial and sub-equitorial rain forest exist that must remain the main target of this approach. Norway is setting up an arrangement with Guyana to safeguard their forests but elsewhere (Indonesia, Brazil etc) have such population and commercial pressures on their forests that it is extremely difficult, and is undermined by black-market activity.
That is why the oceans remain the most likely future engineered carbon sinks (as I discussed previously in Crikey, lin below). There are vast stretches of the Pacific with very little life because they lack one key nutrient, iron, so that seeding them is feasible and cheap. Of course something like this will never be straightforward and might take decades to even assess how to do it or if it is possible, or there is no adverse effect. And certainly any such scheme does not remove the need for the planet to stop adding to the atmospheric load of CO2.
(crikey.com.au/2010/06/11/geoengineering-does-not-remove-the-need-to-decarbonise/)
Geoengineering does not remove the need to decarbonise
by Michael R James Friday, 11 June 2010
Luke Buckmaster here, Crikey website editor.
I have deleted a comment here because it violated our code of conduct.
At Crikey we endorse the technique “to play the ball and not the person.” Please keep this in mind and consult our code of conduct for more info.
we need to cut fossil carbon emissions AND restore lands degraded in the past
– as Michael has said, we need to stop adding to the atmospheric load.
It would not be possible to plant forests over most of the Australian landmass; However, there are many thousands of square kilometres that have been deforested in the past, that could store far more carbon and provide better environmental services than they currently do. For example, this is the focus of the CATER research in QLD:
Fensham RJ & GP Guymer (2009). Carbon accumulation through ecosystem recovery. Environmental Science
and Policy 12: 367-372
Bio-sequestration through restoration of ecosystems is essential, but this has to be _in addition_ to de-carbonising our societies, not as a substitute for it.
Crucially, the fossil fuels we emit had previously been sequestered OUT of the biosphere’s carbon cycle for millions of years.
Releasing fossil carbon into the present land-atmosphere cycle by burning fossil fuels is forcing up atmospheric concentrations at extreme rates of change. Living ecosystems cannot draw down CO2 into biomass or soils fast enough or for long enough to allow fossil fuel emissions to continue, and we need to move as quickly as possible to cut those emissions.
Regarding ocean biosequestration, there is a lot of potential for restoring mangroves, wetlands and other coastal and marine habitats for a range of objectives including carbon sequestration; but the risks involved in large-scale ocean fertilisation experiments are huge and its potential benefits are very small relative to current or projected emissions:
Intergovernmental Oceanographic Commission (2011) Ocean fertilization: A scientific summary for policymakers. UNESCO. Downloadable from: http://unesdoc.unesco.org/images/0019/001906/190674e.pdf.
The report outlines the findings from the 15 ocean fertilisation experiments carried out so far. … there is little information on long-term effects on zooplankton and other marine life. In addition, recent calculations predict that over the course of a century, global-scale ocean fertilisation could sequester, at most, 75 gigatonnes (5 per cent) of the predicted 1500 gigatonnes of carbon that would be emitted from the burning of fossil fuels under a business-as-usual scenario during that time… Currently, there is insufficient evidence to say that ocean fertilisation would not cause any harm to marine ecosystems in the long-term to consider it as a relevant climate change abatement measure.
Very interesting, Dr. Glikson, thanks. And, depressing. Lest we all feel too hopeless, even though we are committed on a warming path, action now will avert disaster later – and be cheaper.
@Boxing Candle: Australia can’t support significant forests. Full stop. However, one of the great successes in the last round of climate talks at Cancun was to speed up the implementation of REDD – which will involve compensating tropical nations for not deforesting their countries. How well that will play out in reality remains to be seen as, for example, there have already been a raft of carpet-baggers in PNG trying to get-rich-quick off the scheme. But let’s hope.
Forests can grow back eventually, the real problem remains that we are burning up a carbon source that has remained locked under the crust for millions of years, and if you can propose a mechanism that doesn’t involve putting a price on carbon and shifting our consumption away from fossil fuels, I’ll … well I don’t know what because you can’t and no one else can. Unfortunately, the scientific reality doesn’t seem to match our social ability to change, but the difficulty of the challenge does not take away from its necessity.
Soil sequestration, geo-sequestration, geo-engineering, tree planting, these are all window-dressing at best, and desperate efforts that may have their own bad consequences at worst. And, as you say, Michael James, will take decades to have any effect.