Can human activity impact the global climate and atmosphere?

This is a highly debated question, though current research points at some strong conclusions. To answer this question well, let us consider the following sub-questions…

What is the chance that human green house gas (GHG) emissions are not the cause of observed global warming?

According to the vast majority of scientific research, it is certain that human activity is creating climate change. Though significant political pressure and press coverage is dedicated to theories that anthropogenic greenhouse gas emissions are not to blame for global warming, or that global warming is related to reasons other than GHG emissions, no scientific peer reviewed publications dispute the fact of humans have caused climate change. The physical laws underlying the greenhouse effect are fully understood and can easily be reproduced in simple lab experiments, the only uncertainties involve the expected response of the climate system to increasing amounts of energy trapped in the world’s atmosphere. While ‘climate skeptics’ make arguments against the observed realities, there is little to no evidence to support their claims.

Looking at the arguments of so called climate sceptics is revealing a level of inaccuracy, ignorance or even intentional distortion equivalent to scientific fraud. Most arguments still in use have been circulating in the early 1990ties and have been countered by intensive research worldwide since, or raise sensationalist rumors in the’ yellow press’. The more sophisticated ones tend to have the following issues:

1 – The data sets used are unreliable or wrong

This was the favored argument used during the late 20thiest century with claims that measurements, and datasets used to calculate global averages, are unreliable. This argument has exhausted itself by thousands of independent observations of climate and climate related phenomena such as vegetation periods, melting glaciers, melting polar ice, increasing ocean temperatures and shifting ecosystem compositions, all supporting and confirming that global temperatures are rising rapidly. So far, 14 out of the 15 years of the 21^st century are the hottest years ever observed and those data are independently confirmed by ground based measurements, ocean temperatures, and satellite based measurement technologies.

2 – Claim that fighting climate change will reduce growth and inhibit development

This argument was widespread in the 20thiest century, and remains the favorite of right wing politicians, but is rapidly losing its appeal in the face of increasing climate related disaster costs, and the dramatic success of alternative energies that start to outcompete fossil fuel derived energy generation. The last prominent climate sceptic of any stature is Bjørn Lomborg who has published a highly controversial best-seller, The Skeptical Environmentalist (2001), claiming that maintaining economic growth for promoting development and health is more important than investing in fighting climate change. This may have been a valid argument in the 20tiest century but has exhausted itself by recent developments showing that green-tech and alternative energies have become the fastest growing sectors in many economies, including the developing world. Instead of modifying his controversial views however, he has as recently as 2012 claimed that “Global warming is by no means our main environmental threat,” an argument no longer tenable considering the large number of high probability and certain negative impacts of global warming observed and strengthening worldwide.

3 – Distortion of scientific information by press or politicians

Falsification or distortion of scientific work in the daily or popular press is another common tool to promote climate skepticism. In a commentary published in the ‘Telegraph’ in 2004 changing solar output rather that greenhouse gases are blamed for global warming.

However, the title is completely misleading in relation to the content of the piece while the scientists interviewed try to provide the true differential picture. The scientific community was quick publishing below figure that shows a perfect match of predictions with expected warming when known solar cycles are overlaid with the forcing effect of increasing greenhouse gas concentrations (Fig. 16). Unfortunately the only thing often remaining in the minds of the general public are the first ‘yellow’ headlines, so that climate skepticism stays far more popular among the wider public than in the scientific community.

Has land degradation in the course of history caused as much greenhouse gases as the use of fossil fuels?

Since the onset of human civilization land degradation has caused release of carbon dioxide into the atmosphere exceeding the amounts released by burning of fossil fuels (see also Emissions Rehabilitation). As assessed by Ruddimann, almost all current deserts (most of the black areas in Figure 17) have as a fact been dramatically degraded already thousands of years ago by human activity and are de facto man-made.

Recent archaeological research seems to confirm this and implies a direct interaction between land degradation, ecosystem collapses and the demise of whole civilizations – see:

The Middle East was likely heavily degraded already 5000 years ago, due to wood and food demand of early civilizations causing massive deforestation and erosion. Fig. 18 presents an example of highly degraded semi-arid hill country in the Judean Mountains, with soil completely washed away by land degradation and erosion as depicted by Plato in his dialogue “Critias”. A plot restored by pine afforestation indicates that even such mostly exposed rock badlands can be restored to productive ecosystems within a few dozen years.

We use here the same picture to demonstrate the impacts of such land degradation or restoration on atmospheric greenhouse gas concentration. Land degradation, deforestation and desertification release large amounts of CO₂ into the atmosphere from biomass burning, and oxidation of soil organic matter. According to various sources, hundreds of Gigatons of carbon in the form of CO₂ were transferred into the atmosphere by human induced land use change, more than was emitted so far by fossil fuel combustion. The young 5 hectare pine wooded area (Fig. 19) stores about 1000 tons of carbon dioxide recovered from the atmosphere in new soil and biomass, and will continue sequestering 6- 8 tons of CO₂ per hectare and year for dozens of years to come.

This means that each hectare of degraded dryland can sequester hundreds of tons of the greenhouse gas CO₂ from the atmosphere. Considering that billions of hectares of such degraded dryland exists, as well as similar amounts of other degraded ecosystems, biological carbon sequestration into restored ecosystems can counter a very significant part of the greenhouse gas emissions currently caused by fossil fuel burning into recovering vegetation and soils (see the model calculation in chapter 4).

How great are the impacts of human land use on GHG emissions?

Current emissions from deforestation are still around 16% of total greenhouse gas emissions. Unfortunately this does not include a reliable estimate of greenhouse gas emissions from soil degradation and desertification that will add to this number.

As illustrated in Fig. 20, all the world’s ecosystems are subject to ongoing degradation processes that continue emitting greenhouse gases into the atmosphere. Interestingly, all knowledge to avoid further such degradation and greenhouse gas emissions, or even to create huge areas of carbon sequestering recovering ecosystems, is available and has been successfully applied, e. g. in parts of China or Europe. A decisive biosphere protection and rehabilitation program could in fact temporarily sequester so much greenhouse gases to stop their accumulation in the atmosphere.

As figure 21 clearly demonstrates, that various developing countries, e. g. Malaysia, Indonesia, most of South America and parts of Southern and Central Africa, become major GHG emitters with higher per capita emissions than any European countries, if their land-use change emissions are being considered. This is not only bad for the climate, it also reduces ecosystem resilience in those often humid areas and leads to floods, landslides, and droughts together with dramatic loss in biodiversity.

Can land rehabilitation by restoration of degraded ecosystems mitigate global warming?

Yes. Several different parallel mechanisms associated with land rehabilitation could contribute to mitigating global warming. The information below includes a number of these, particularly relating to GHG sequestration into biomass and soil:

Applying the same principles to all degraded semi arid regions world wide could create a carbon sink of around 100 Gt (350 Gt CO2)! Including rehabilitation of degraded arid, sub-humid and degraded more humid ecosystems areas, a multiple of that amount could be sequestered while increasing biological biomass productivity.

This subject has been widely discussed and elaborated in the scientific literature by major research teams, and is widely accepted even by IPCC. The extent to which such actions could be funded by carbon trading was poorly arranged until recently, though the recent REDD mechanism should offer compensation more easily.

Unfortunately, soil carbon sequestration, which is the largest sink potential in dryland and agricultural soils has yet to be included in such funding schemes, even though the clear correlation of carbon sequestration with enhanced productivity and ecosystem resilience has been widely demonstrated. The most prominent proponent and former member of IPCC is Prof. Rattan Lal, who has written multiple high impact publications on the importance of soil restoration and carbon sequestration for enhancing food security and mitigating climate change, for example:

R. Lal (2004) Soil Carbon Sequestration Impacts on Global Climate Change and Food Security, Science 11 June 2004: Vol. 304 no. 5677 pp. 1623-1627. DOI: 10.1126/science.1097396.

Abstract – The carbon sink capacity of the world’s agricultural and degraded soils is 50 to 66% of the historic carbon loss of 42 to 78 gigatons of carbon. The rate of soil organic carbon sequestration with adoption of recommended technologies depends on soil texture and structure, rainfall, temperature, farming system, and soil management. Strategies to increase the soil carbon pool include soil restoration and woodland regeneration, no-till farming, cover crops, nutrient management, manuring and sludge application, improved grazing, water conservation and harvesting, efficient irrigation, agroforestry practices, and growing energy crops on spare lands. An increase of 1 ton of soil carbon pool of degraded cropland soils may increase crop yield by 20 to 40 kilograms per hectare (kg/ha) for wheat, 10 to 20 kg/ha for maize, and 0.5 to 1 kg/ha for cowpeas. As well as enhancing food security, carbon sequestration has the potential to offset fossilfuel emissions by 0.4 to 1.2 gigatons of carbon per year, or 5 to 15% of the global fossil-fuel emissions.

R. Lal (2004), Soil carbon sequestration to mitigate climate change Geoderma Volume 123, Issues 1–2, November Pages 1–22.

Abstract – The increase in atmospheric concentration of CO₂ by 31% since 1750 from fossil fuel combustion and land use change necessitates identification of strategies for mitigating the threat of the attendant global warming. Since the industrial revolution, global emissions of carbon (C) are estimated at 270±30 Pg (Pg=petagram=10¹⁵ g=1 billion ton) due to fossil fuel combustion and 136±55 Pg due to land use change and soil cultivation. Emissions due to land use change include those by deforestation, biomass burning, conversion of natural to agricultural ecosystems, drainage of wetlands and soil cultivation. Depletion of soil organic C (SOC) pool have contributed 78±12 Pg of C to the atmosphere. Some cultivated soils have lost one-half to two-thirds of the original SOC pool with a cumulative loss of 30–40 Mg C/ha (Mg=megagram=10⁶ g=1 ton). The depletion of soil C is accentuated by soil degradation and exacerbated by land misuse and soil mismanagement. Thus, adoption of a restorative land use and recommended management practices (RMPs) on agricultural soils can reduce the rate of enrichment of atmospheric CO₂ while having positive impacts on food security, agro-industries, water quality and the environment. A considerable part of the depleted SOC pool can be restored through conversion of marginal lands into restorative land uses, adoption of conservation tillage with cover crops and crop residue mulch, nutrient cycling including the use of compost and manure, and other systems of sustainable management of soil and water resources. Measured rates of soil C sequestration through adoption of RMPs range from 50 to 1000 kg/ha/year. The global potential of SOC sequestration through these practices is 0.9±0.3 Pg C/year, which may offset one-fourth to one-third of the annual increase in atmospheric CO₂ estimated at 3.3 Pg C/year. The cumulative potential of soil C sequestration over 25–50 years is 30–60 Pg. The soil C sequestration is a truly win–win strategy. It restores degraded soils, enhances biomass production, purifies surface and ground waters, and reduces the rate of enrichment of atmospheric CO₂ by offsetting emissions due to fossil fuel.

The Yattir Forest research group of Prof. Dan Yakir has published a wide range on carbon sequestration and other impacts of dryland afforestation

J. M. Grünzweig et al, Carbon sequestration in arid-land forest Global Change Biology: Volume 9, Issue 5, 2003, Pages 791–799

Abstract – Rising atmospheric CO₂ concentrations may lead to increased water availability because the water use efficiency of photosynthesis (WUE) increases with CO₂ in most plant species. This should allow the extension of afforestation activities into drier regions. Using eddy flux, physiological and inventory measurements we provide the first quantitative information on such potential from a 35-year old afforestation system of Aleppo pine (Pinus halepensis Mill.) at the edge of the Negev desert. This 2800 ha arid-land forest contains 6.5 ± 1.2 kg C m⁻², and continues to accumulate 0.13–0.24 kg C m⁻² yr⁻¹. The CO₂ uptake is highest during the winter, out of phase with most northern hemispheric forest activity. This seasonal offset offers low latitude forests ∼10 ppm higher CO₂ concentrations than that available to higher latitude forests during the productive season, in addition to the 30% increase in mean atmospheric CO₂ concentrations since the 1850s. Expanding afforestation efforts into drier regions may be significant for C sequestration and associated benefits (restoration of degraded land, reducing runoff, erosion and soil compaction, improving wildlife) because of the large spatial scale of the regions potentially involved (ca. 2 × 10⁹ ha of global shrub-land and C4 grassland). Quantitative information on forest activities under dry conditions may also become relevant to regions predicted to undergo increasing aridity.

A wide range of other publications confirm and detail on the above publications. Unfortunately so far, soil carbon sequestration has not been included in accepted climate mitigation options, even though this potential is by far the largest in agricultural and dry ecosystems.

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