acidification (Nathan et al. 2008; Siddall et al. 2009).
Over the last decade, multiple long‐term climate shifts have been observed in regional, continental and ocean basin scales, including major changes in Arctic and ice temperatures, heavy precipitation, increased salinity of the seas, altered wind patterns severe events such as drought, and heat waves. Over the last 100 years, normal temperatures have risen in the Arctic region to about twice the global average. In addition, after 1978, satellite data show that the average Arctic sea ice expansion decreased by 2.7%, from 2.1 to 3.3% per decade, with even greater decreases of 7.4%, from 5.0 to 9.8% per decade during the summer (Gregory et al. 2002).
Released in April 2007 (IPCC 2007; Climate Change 2007: Impacts, Adaptation and Vulnerability), the IPCC (Climate Change 2007: Impacts, Adaptation and Vulnerability) report discusses the imminent effects of global warming on human society and ecosystems and outlines scenarios up to 2100. Many effects on the natural environment have already started to emerge as a result of human activities, including improvements in the management of agriculture and forestry in higher latitude areas of the Northern Hemisphere, the timing of planting and growing spring crops, and shifts in pattern disturbance due to fires and pests. Human settlements in mountainous areas, in particular, are at greater risk of floods due to the disruption of glacial lakes caused by glaciers melting. The new IPCC report in September 2019 emphasized that the rate of ocean heating has risen twice as much since 1993 as the initial and consequent melting of the two historic ice sheets covering West Antarctica and Greenland, which has also increased the sea level. Alarmingly, the western Antarctic glaciers may have been so weak that they may have hit the point of no return (IPCC 2019). Rising sea levels pose a major threat to low‐lying coastal areas, home to almost 680 million people, comprising around 10% of the world’s population.
In conjunction with warmer conditions in the Sahel region of Africa, the eruption of drought has reduced the length and duration of the growing season. Therefore, this dense population area, where adaptive capacity is relatively low, is particularly vulnerable to challenges such as tropical storms or the decline of local coasts. The number of people affected will be higher in the large deltas in Asia and Africa, while small islands are particularly vulnerable because of their isolation. Overall, from a health perspective, there will be a rise in the number of deaths from illnesses and injuries caused by heat waves, hurricanes, floods, droughts, fires, etc. as well as an increase in the incidence of respiratory diseases and the spread of some vectors of infectious diseases due to higher ozone concentrations usually associated with climate change. The extent of the adverse effects will be proportional to the mean global increase in temperature. Even though relative to almost pre‐industrial levels, the phenomenon of global warming is limited to 2 °C, harmful effects will be evident, and the planet will be forced to take drastic measures to adjust to current climate conditions. Suppose the increase in temperature crosses the 2 °C mark amid global efforts, in that case, it will lead to an unprecedented situation in which the consequences would certainly have been extreme, widespread and catastrophic.
Renewable water supply is threatened by declines in some areas and expansions in others, both of which are equally significant. In regions where gains are expected, temporary water deficiencies are still possible due to increased flux variability and seasonal shortages (due to reduced accumulation of snow and ice). Clean and fresh water supplies can also decline due to lower water quality caused by warm weather, such as algae‐producing toxins, which could degrade the quality of critical sources such as lakes. Such a decline in renewable water supply will exacerbate competition between agriculture, towns, industry and water energy production, impacting local water, food and energy security. In addition, rising sea levels would have major consequences alongside coasts, including flooding, coastal erosion and submergence of low‐lying areas, posing severe risks to residents, infrastructure, habitats and near‐shore vegetation. Low‐lying regions (e.g. Bangladesh) and islands as a whole, such as the Maldives and Kiribati, are at risk of near‐term destruction due to various factors such as rising ocean levels, floods and extreme storms.
Over the past millions of years, climate change has occurred progressively and slower, allowing ecosystems to adapt. However, since the early twentieth century, species’ extinction rate has risen to more than 100 times the normal rate, i.e. without anthropogenic interference. As a result, we are in the midst of a major biodiversity crisis and may even head towards another mass extinction (Mendenhall et al. 2014). The current rapid changes are suggested to impact both land and ocean ecosystems by 2050. Ecosystem changes, however, include much more than climate change, and a combination of many factors, including urbanization, increased world population and others, causes significant extinctions. However, climate change has shown its impact and will only intensify with time.
Over the past millions of years, climate change has occurred steadily and slowly, allowing ecosystems to adapt. However, since the beginning of the twentieth century, organism extinction rates have risen to more than 100 times the normal rate, i.e. without anthropogenic interference. As a result, we are in the midst of a major biodiversity crisis and maybe even head towards another mass extinction (Mendenhall et al. 2014). It is proposed that by 2050, rapid changes are likely to impact both land and ocean ecosystems.
1.5.2 Process and Causes of Global Warming
The earth gets enough space from radiation coming from the sun. To hold Earth’s temperature at an optimal level, greenhouse gases play a crucial role in trapping the solar heat needed to sustain life. This phenomenon is natural, known as the greenhouse effect, and therefore important for sustaining various life forms on Earth. Without the greenhouse effect, Earth’s temperature would be around 33 °C lower than it is today (Morice et al. 2012). Human activities have led to substantial increases in atmospheric GHGs due to deforestation and high fossil‐fuel combustion rates in recent decades. Over the last century, GHG production is the primary cause of global warming. Earth warming ranged from +0.8 to +1.0 °C after 1900, according to published literature (Figure 1.3; den Elzen and Meinshausen 2006). Since 1950, land‐only observations have shown warming trends between +1.1 and +1.3 °C, as land temperatures usually react rapidly in the climate change phase compared to oceans. Various factors affect the Earth’s climate, including solar (warming effect), volcanic eruptions (and their cooling effect) and atmospheric GHG levels (warming effect). Methane‐led carbon dioxide (CO2) has been a significant contributor to global warming since the Industrial Revolution of 1750, with CO2 concentrations rising from 278 parts per million (ppm) in 1960 to nearly double at 401 ppm in 2015 (Levitus et al. 2005). Since 1951, almost 100% of the warming is due to anthropogenic activities. Human activities are now responsible for increasing global temperatures by 1.1 °C, and according to reports, global emissions are already heading towards 1.5 °C or near‐mid‐century targets.
Figure 1.3 Instrumental temperature data 1880–2014.
Source: NASA Goddard Institute for Space Studies (GISS).
Because of an increase in GHG concentrations, water vapour has a significant indirect impact on temperature changes. High global temperatures increase the atmosphere’s ability to absorb water vapour due to GHGs, which increases temperature, as water vapour also contributes to the greenhouse effect. Thus, an increase of 1 °C in global temperature results in an increase in atmospheric water vapour by around 7%. Therefore, it is clear that while CO2 is the primary candidate for anthropogenic climate, water vapour amplifies the effect and is, therefore, a central agent of climate change (Gillett and Matthews 2010). Limiting global warming to below 2 °C worldwide is widely seen as an effective aim to reduce dangerous warming. Still, it is unlikely to be achieved without major reductions in GHG emissions (Canadell 2007). More than 100 countries have agreed on a global warming limit of 2 °C or less as a benchmark for mitigation steps to reduce the risks, impacts and damage caused by climate change (relative to pre‐industrial levels).