What is Global Warming or Climate Change and what are its causes and risks?

You are here: Home / Ecosystem Restoration Learning Modules / What is Global Warming or Climate Change and what are its causes and risks?

This issue is quite wide and touches on topics larger than Project Wadi Attir, but to understand the impacts of this question for the globe, the relationship of local actions to the whole, and what we are doing to mitigate problems, let us consider the following sub-questions…

Is global warming caused by an increase of greeenhouse gas concentration in the atmosphere due to human activity?

According to scientific evidence, this is certainly the case. The temperature on earth is balanced by earth’s own heat generation, earth’s albedo (the relative amount of sunlight absorbed versus the amount of radiation reflected back into space), and by the amount of heat radiation emitted from earth that is trapped in the atmosphere by so called greenhouse gasses (Fig. 1). The most powerful greenhouse gasses are carbon dioxide (CO₂), methane, nitrous oxide (N₂O), water vapor, and synthetic human made chlorinated fluorocarbons (CFCs) that were produced and emitted in huge amounts during the last century and caused ozone depletion as well as global warming.

Fig. 1: Schematic representation of earth’s energy budget

The earth’s climate system is in no ways stable, and has been subject to dramatic variations during millions of years often for unknown reasons. The solar cycles, small changes in earth’s orbit, plate tectonics altering global albedo or ocean currents all may induce dramatic climate fluctuations. The series of coming and going ice ages provide a stern warning that earth’s climate system is highly labile.

Concentrations of greenhouse gases in the atmosphere play a central role in determining earth’s temperature. As determined from ice cores, atmospheric CO₂ concentrations have fluctuated between 200 and 250 ppm (parts per million) during the last 800000 years while earth repeatedly entered and exited the various ice ages. Human activity has likely started affecting global climate during the last 10000 years. Widespread domestication of farm animals, deforestation, agriculture and certainly rising bush fire frequencies resulted in growing concentrations of carbon dioxide in the atmosphere inducing a relative warming (see below publication for detailed information).

This process was accelerated dramatically during the industrial revolution when mankind started using fossil fuels such as coal, oil, and natural gas, and human population started to increase exponentially leading to massive land clearing for agriculture. During the last 200 years however, atmospheric carbon dioxide concentrations started growing at extreme speed, reaching 400 ppm in 2014 and rising further beyond anything observed in the last million years. The slope of this increase is so dramatic, that it is not resolved in the graph in figure 2 showing atmospheric CO₂ concentrations over the last 800000 years.

Consider this text about the Anthropogenic Greenhouse Era to learn more

Fig. 2: Atmospheric CO₂ concentrations during the last 800000 years. Concentrations around 200 ppm are correlated with ice ages, while concentrations around 250 ppm are correlated with interglacial periods. The human induced increase in recent history is indicated by the line to the right leaving the scale at 400 ppm.

Earth’s temperature increased in parallel with this rise in greenhouse gases. Today’s temperatures are 1^oC higher than in the 19^th century (Fig. 3), and another degree of warming is expected within the next 50 years, which is unavoidable based on current trends.

Fig. 3: Global average temperatures recorded during the last 130 years. The world cheats itself by placing a baseline around 1960, which is already at least 0.3 degrees warmer than the 19^th century average.

Methane is a second, major greenhouse gas accumulating in the atmosphere due to human activity (Fig. 4). Though its concentrations are lower, it is a 25 times more powerful greenhouse gas than CO₂ and therefore also contributes significantly to global warming. The major initial methane increase was apparently caused by cattle herding that started increasing atmospheric methane concentrations during the last 4000 years. The major boost towards exponentially growing atmospheric methane concentrations coincides with the beginning of the industrial age, with rapidly increasing populations, farming activity, growing waste and waste water problems, and mining for fossil fuels initiating a rapid and massive increase in atmospheric methane concentrations.

Methane emissions are a co-driver and a major risk factor to global climate.

Fig. 4: Atmospheric methane concentrations during the last 10000 years as measured from ice core data (red dots) and directly in the atmosphere (blue line), compared to data from a similar 10000 years period 100000 years ago (green dots). Exponentially increasing concentrations since the beginning of the industrial age are contributing near 20 % to global warming observed.

Can the consequences and risks of global warming be far reaching or even disastrous?

Unfortunately, yes. Global warming has been and is causing with increased frequency and intensity a wide range of changes in the earth’s climate, ecology, agriculture, and for example has been causing a wide range of lethal heatwaves in various locations. A view of a few of the most worrisome examples and their levels of certainty are listed below:

Sea Level Rise – Certain and Unavoidable:

Sea level rise is a certain and unavoidable consequence of global warming with enormous future impact. Current models predict up to 2 m of sea level rise during this century (Fig. 5); again the models used are anything but adequate leaving high degrees of uncertainty.

The most recent NASA assessments include the following stern warning:

1 – Sea levels will rise by 1m or more in this century.
2 – This cannot be avoided anymore, rather is a result of current warming observed.
3 – Major cities such as Tokyo or Singapore are under threat of massive flooding.
4 – 150 million people are threatened by such sea level rise.
5 – If warming continues at current rates, much greater sea level rise may occur rapidly.

Fig. 5: predicted sea level rise during the 21^st century according to various models and scenarios.

This may not seem much, however, dense population of coastal areas means that hundreds of millions will be affected by a few meters of sea level rise, as demonstrated in the following animation by the USGS:

Altered Water Balances – Certain:

Much of the globe is expected to receive same or higher precipitation in a warming world. However, Australia, the Mediterranean Basin and the Middle East, Southern Africa and North and Central America are predicted to experience very significant reductions in rainfall and available freshwater runoff (Fig. 6). Considering that those are some of the most productive farmlands worldwide, extremely serious implications for global food security must be predicted.

Fig 6: Illustrative map of future climate change impacts related to freshwater which threaten the sustainable development of the affected regions. Areas with blue colors indicate the increase of annual runoff, areas in red indicate a decrease

A recent NASA prediction (Fig. 7) projects very significant loss of average soil humidity in the US and Canada, the world’s bread baskets, during the next eighty years with dramatic consequences on US and world grain production and global food security.

Fig. 7: Changes in soil moisture in North America in 2095 compared to current levels as predicted by NASA. Brown colors indicating a decrease, and blue colors an increase in average soil moisture expected.

This model is based on expected increases in temperatures as well as changes in precipitation expected.

Melting of Polar Ice Caps – Certain

The melting of polar ice caps due to global warming is a major concern because it will cause dramatic sea level rise, as well as changes in ocean currents, ocean chemistry, polar climate and ecology with unpredictable but possibly disastrous consequences. Arctic sea ice (Fig 8), the Greenland ice sheet, and the West Antarctic ice sheet already now reveal signs of disintegration and collapse leading to massive sea level rise, a process that is unstoppable in the short term.

Besides sea level rise, the loss of the polar ecosystems including large populations of polar bears, seals and sea birds is almost unavoidable, and climatic changes induced by large exposed rock and ocean surfaces are impossible to predict, but may be far reaching and dramatic.

Fig. 8: Observed loss in Arctic Sea ice cover exceeds IPCC models, and the most daring predictions indicate almost complete loss of Arctic sea ice within 10 years, but with high probability until 2050.

Poorly understood but potentially disastrous mechanisms – lower probability, ultra-high risks

Hidden methane reserves represent a very serious though not quantifiable risk for triggering a dramatic, rapid and irreversible disastrous global warming effect in case massive reserves tied down in permafrost and as ice clathrates in arctic oceans would be rapidly released due to further global warming.

Such a methane triggered warming event is implicated in the worst mass extinction earth has seen so far, 251 million years ago. This should be a stern warning for things to come, as indeed current warming rates may trigger massive release of methane resulting in an uncontrollable runaway greenhouse.

Other very high risk scenarios are currently considered unlikely as well, with less than 10% probability, but considering the possible disastrous consequences this may represent a major risk especially as the underlying science and modelling are incomplete and inadequate. As stated above, the world climate system is tightly controlled by ocean currents and global wind circulations. The El Nino events happening in irregular intervals for example are triggered by warm surface waters in the Pacific Ocean and dramatically alter climate and precipitation patterns around the world. A more frequent occurrence of this phenomenon, could do grave damage to the world’s agriculture, fisheries, and ecology, and is predicted by various models.

Is global warming mainly caused by the burning of fossil fuels for energy generation?

Actually, no. During much of human history, land use change, meaning transformation of natural ecosystems to farmland and pasture, and increasing numbers of cattle and livestock, have contributed more greenhouse gases to the atmosphere than the burning of fossil fuels.

Even today, fossil fuels use contributes only 57% to the increase of GHGs in the atmosphere, the reminder derived from land use change, waste and livestock in the form of methane, and other greenhouse gases produced by agriculture and industrial processes.

Fig. 9: Contribution of different greenhouse gasses to global warming and their origin.

At the global scale, the key greenhouse gases emitted by human activities (Fig. 9) are:

Carbon dioxide (CO₂), Methane (CH₄), Nitrous oxide (N₂O), Fluorinated gases (F-gases) which include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). Black carbon (BC) is a solid particle or aerosol, not a gas, but it also contributes to warming of the atmosphere. Learn more about BC and climate change on this Causes of Climate Change page.

Have land use change and agriculture been the major contributors to increasing atmospheric greenhouse gas concentrations?

Agriculture has been and still is the major contributor to increasing greenhouse gas concentrations in the atmosphere. Growing mechanization, growing fertilizer use (1 kg ammonia = 3 kg CO₂); and increasing soil degradation enhance GHG concentrations in the atmosphere. Globalization and liberalization of trade in farm products has increased transport routes, and induced huge rates of deforestation. Worst of all, growing consumption of animal products requires exponentially increasing production of fodder and water at the expense of environmental degradation and GHG emissions.

Including fossil fuel use for food and feed production, harvesting and transport, it is fair to assume that about 50% of anthropogenic GHG emissions are linked to agriculture and forestry. Those emissions are far less efficiently tackled than energy related emissions. Intensive livestock breeding, deforestation, land degradation and desertification therefore continue releasing growing amounts of greenhouse gases into the atmosphere. Consequently and not surprisingly potential emissions saving in the agriculture and forestry sectors are the biggest and most worthwhile available for immediate reductions. Out of over 20 billion tons of CO₂equivalents emissions per year that have to be saved in the near future over 9 billion can be derived from sustainable forestry, agriculture and waste management (Fig.10). Project Wadi Attir addresses all three sectors equally for maximally sustainable dryland development.

Fig.10: Among the available mitigation options agriculture and forestry offer almost 50% of the total rapidly achievable GHG emissions reductions for achieving the target of below 2^oC global warming.

Specifically, sustainable farming techniques can dramatically reduce anthropogenic (human caused) greenhouse gas emissions, by application of agroforestry, soil rehabilitation, no till agriculture and similar. Soil restoration can enhance soil organic carbon by several hundred Gigatons, and reforestations could sequester a similar amount of carbon dioxide into biomass. For further reading, consider the two manuscripts attached.

Try this quiz and test your knowledge of the question: