Shedding light on Climate Change: its evidences and its consequences

The chapter 2 of the World Bank report “Turn down the Heat” is a key tool to understand the climate change and provides a general overview of its main consequences, but it is not easily accessible to general public because of its length and its technical approach. This summary aims to get close the main points, focusing on the main evidences of human-induced climate change and connect them with its main consequences.

  1. The Rise of CO2 concentrations and emissions
  2. Rising global mean temperature
  3. Increasing Ocean Heat Storage
  4. Increasing loss of ice from Greenland and Antartica
  5. Rising Sea Levels
  6. Ocean Acidification
  7. Drought and Aridity

1.  The Rise of CO2 concentrations and emissions

One of the most noticeable evidences of global warming is the substantial rise of temperatures. Furthermore, “most of the observed increase in global average temperature since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” (Solomon, Miller et al. 2007).

2. Rising global mean temperature

Global mean warming is now approximately 0.8°C above preindustrial levels and a suite of studies confirms that the observed warming cannot be explained by natural factors. In fact, the IPCC (2007) states that during the last 50 years “the sum of solar and volcanic forcings would likely have produced cooling, not warming (Wigley and Santer 2012).

CONSEQUENCE: The most tangible evidences are heat waves and extreme temperatures.

These events were highly unusual with monthly and seasonal temperatures typically more than 3 standard deviations warmer than the local mean temperatura. The five hottest summers in Europe since 1500 all occurred after 2002.

In the 1960s, summertime extremes of more than three standard deviations warmer than the mean of the climate were practically absent, affecting less than 1 percent of the Earth’s surface. Now such extremely hot outliers typically cover about 10 percent of the land area (Hansen et al. 2012). The above analysis implies that extremely hot summer months and seasons would almost certainly not have occurred in the absence of global warming. Heat waves often caused many heat-related deaths, forest fires, and harvest losses

3. Increasing Ocean Heat Storage

As a consequence of the previous evidence, oceans have stored a very high amount of heat. Approximately 93 percent of the additional heat absorbed by the Earth system is stored in the ocean. Between 1955 and 2010 the world’s oceans, to a depth of 2000 meters, have warmed on average by 0.09°C.

CONSEQUENCES: warming waters are expected to adversely affect fisheries, particularly in tropical regions as stocks migrate away from tropical countries towards cooler waters (Sumaila 2010). Furthermore, warming Surface waters can enhance stratification, potentially limiting nutrient availability to primary producers. Another particularly severe consequence could be the expansion of ocean hypoxic zones. Reductions in the oxygenation zones of the ocean are already occurring, and in some ocean basins have been observed to reduce the habitat, such as tuna.

4. Increasing loss of ice from Greenland and Antartica

Another consequence of the rise of temperatures is the increasing loss of ice from poles. A recent estimate by Church et al. in 2011 gives 1.3 ±0.4 mm/year for the period 2004–08, estimated from a combination of satellite gravity measurements, satellite sensors, and mass balance methods. At present, the losses of ice are shared roughly equally between Greenland and Antarctica.

(Rignot et al. 2011) points out that if the present acceleration continues, the ice sheets alone could contribute up to 56 cm to sea-level rise by 2100.

CONSEQUENCES: The main consequence is the rise of sea levels, which is by itself remarkable evidence and is shown on the next point. Apart of that, among the potential impacts are changes in the dominating air pressure systems since the heat Exchange between ocean and atmosphere increases as the ice disappears, large-scale wind patterns can change and extreme winters in Europe may become more frequent (Francis and Vavrus 2012).

5. Rising Sea Levels

Updated estimates and reconstructions of sea-level rise, based on tidal gauges and more recently, satellite observations, confirm a sea-level rise of more than 20 cm since preindustrial times7 to 2009 taking in account the rise caused by melting of mountain glaciers. The rate of sea-level rise was close to 1.7 mm/year during the 20th century, accelerating to about 3.2 mm/year on average since the beginning of the 1990s (Meyssignac and Cazenave 2012).

There are significant regional differences in the rates of observed sea-level rise because of a range of factors, including differential heating of the ocean, ocean dynamics (winds and currents), and the sources and geographical location of ice melt, as well as subsidence or uplifting of continental margins.

6. Ocean Acidification

The oceans play a major role as one of the Earth´s large CO2 sinks. As atmospheric CO2 rises, the oceans absorb additional CO2 in an attempt to restore the balance between uptake and release. They have taken up approximately 25 percent of anthropogenic CO2 emissions in the period 2000–06 (Canadell et al 2007). CO2 reacts with water to eventually form a weak acid. Observed increases in ocean acidity are more pronounced at higher latitudes than in the tropics.

CONSEQUENCE: The reaction of CO2 with seawater reduces the availability of carbonate ions that are used by various marine biota for skeleton and shell formation in the form of calcium carbonate (CaCO3).

7. Drought and Aridity

On a global scale, warming of the lower atmosphere strengthens the hydrologic cycle, mainly because warmer air can hold more water vapour (Coumou and Rahmstorf 2012; Trenberth 2010). This strengthening causes dry regions to become drier and wet regions to become wetter. Increased atmospheric water vapour loading can also amplify extreme precipitation; however, patterns of change are generally more complex because of aerosol forcing and regional phenomenon including soil, moisture feedbacks. Anthropogenic aerosol forcing likely played a key role in observed precipitation changes over the period 1940–2009 (Sun et al. 2012).

A poleward migration of the mid-latitudinal storm tracks, can also strongly affect precipitation patterns. Warming leads to more evaporation and evapotranspiration, which enhances surface drying and, thereby, the intensity and duration of droughts (Trenberth 2010). Aridity (that is, the degree to which a region lacks effective, life-promoting moisture) has increased since the 1970s by about 1.74 percent per decade, but natural cycles have played a role as well (Dai 2010, 2011).

The Mediterranean experienced 10 of the 12 driest winters since 1902 in just the last 20 years (Hoerling et al. 2012). Anthropogenic greenhouse gas and aerosol forcing are key causal factors.

CONSEQUENCE: Apart of the direct impact on human consumption, agriculture would be the most affected sector, which implies phenomena related to food disposal. Since the 1960s, sown areas for all major crops have increasingly experienced drought, with drought affected areas for maize more than doubling from 8.5 percent to 18.6. High impact regions are expected to be those where trends in temperature and precipitation go in opposite directions. At the same time, summertime temperatures have been increasing steadily since the 1970s, further drying the soils because of more evaporation.

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