Introduction to climatic fluctuations and climate change. Climate change over India and World. Issues on global climate change

Climate change is a change in the statistical distribution of weather patterns when that change lasts for an extended period of time (i.e., decades to millions of years).

Climate change may refer to a change in average weather conditions, or in the time variation of weather within the context of longer-term average conditions, defined by the World Meteorological Organization as a 30 years or longer term.

Climate change is caused by factors such as biotic processes, variations in solar radiation received by Earth, plate tectonics, and volcanic eruptions. Certain human activities have been identified as primary causes of ongoing climate change, often referred to as global warming. 

Scientists actively work to understand past and future climate by using observations and theoretical models. A climate record—extending deep into the Earth's past—has been assembled, and continues to be built up, based on geological evidence from borehole temperature profiles, cores removed from deep accumulations of ice, floral and faunal records, glacial and periglacial processes, stable-isotope and other analyses of sediment layers, and records of past sea levels. More recent data are provided by the instrumental record. General circulation models, based on the physical sciences, are often used in theoretical approaches to match past climate data, make future projections, and link causes and effects in climate change.

Factors that can shape climate are called climate forcings or "forcing mechanisms". These can be either "internal" or "external". Internal forcing mechanisms are natural processes within the climate system itself (e.g., the thermohaline circulation). External forcing mechanisms can be either anthropogenic—caused by humans—(e.g. increased emissions of greenhouse gases and dust) or natural (e.g., changes in solar output, the earth's orbit, volcano eruptions).

Physical evidence to observe climate change includes a range of parameters. Global records of surface temperature are available beginning from the mid-late 19th century. For earlier periods, most of the evidence is indirect—climatic changes are inferred from changes in proxies, indicators that reflect climate, such as ice cores, dendrochronology, sea level change, and glacial geology. Other physical evidence includes arctic sea ice decline, cloud cover and precipitation, vegetation, animals and historical and archaeological evidence.

The most general definition of climate change is a change in the statistical properties (principally its mean and spread) of the climate system when considered over long periods of time, regardless of cause. Accordingly, fluctuations over periods shorter than a few decades, such as El Niño, do not represent climate change.

The term "climate change" is often used to refer specifically to anthropogenic climate change (also known as global warming). Anthropogenic climate change is caused by human activity, as opposed to changes in climate that may have resulted as part of Earth's natural processes. In this sense, especially in the context of environmental policy, the term climate change has become synonymous with anthropogenic global warming. Within scientific journals, global warming refers to surface temperature increases while climate change includes global warming and everything else that increasing greenhouse gas levels affect.

A related term, "climatic change", was proposed by the World Meteorological Organization (WMO) in 1966 to encompass all forms of climatic variability on time-scales longer than 10 years, but regardless of cause. During the 1970s, the term climate change replaced climatic change to focus on anthropogenic causes, as it became clear that human activities had a potential to drastically alter the climate. Climate change was incorporated in the title of the Intergovernmental Panel on Climate Change (IPCC) and the UN Framework Convention on Climate Change (UNFCCC). Climate change is now used as both a technical description of the process, as well as a noun used to describe the problem.

On the broadest scale, the rate at which energy is received from the Sun and the rate at which it is lost to space determine the equilibrium temperature and climate of Earth. This energy is distributed around the globe by winds, ocean currents, and other mechanisms to affect the climates of different regions.

Factors that can shape climate are called climate forcings or "forcing mechanisms". These include processes such as variations in solar radiation, variations in the Earth's orbit, variations in the albedo or reflectivity of the continents, atmosphere, and oceans, mountain-building and continental drift and changes in greenhouse gas concentrations. There are a variety of climate change feedbacks that can either amplify or diminish the initial forcing. Some parts of the climate system, such as the oceans and ice caps, respond more slowly in reaction to climate forcings, while others respond more quickly. There are also key threshold factors which when exceeded can produce rapid change.

Forcing mechanisms can be either "internal" or "external". Internal forcing mechanisms are natural processes within the climate system itself (e.g., the thermohaline circulation). External forcing mechanisms can be either anthropogenic (e.g. increased emissions of greenhouse gases and dust) or natural (e.g., changes in solar output, the earth's orbit, volcano eruptions).

Whether the initial forcing mechanism is internal or external, the response of the climate system might be fast (e.g., a sudden cooling due to airborne volcanic ash reflecting sunlight), slow (e.g. thermal expansion of warming ocean water), or a combination (e.g., sudden loss of albedo in the Arctic Ocean as sea ice melts, followed by more gradual thermal expansion of the water). Therefore, the climate system can respond abruptly, but the full response to forcing mechanisms might not be fully developed for centuries or even longer.

Internal forcing mechanisms

Scientists generally define the five components of earth's climate system to include atmosphere, hydrosphere, cryosphere, lithosphere (restricted to the surface soils, rocks, and sediments), and biosphere. Natural changes in the climate system ("internal forcings") result in internal "climate variability". Examples include the type and distribution of species, and changes in ocean-atmosphere circulations.

Ocean-atmosphere variability

The ocean and atmosphere can work together to spontaneously generate internal climate variability that can persist for years to decades at a time. Examples of this type of variability include the El Niño–Southern Oscillation, the Pacific decadal oscillation, and the Atlantic Multidecadal Oscillation. These variations can affect global average surface temperature by redistributing heat between the deep ocean and the atmosphere and/or by altering the cloud/water vapor/sea ice distribution which can affect the total energy budget of the earth.

The oceanic aspects of these circulations can generate variability on centennial timescales due to the ocean having hundreds of times more mass than in the atmosphere, and thus very high thermal inertia. For example, alterations to ocean processes such as thermohaline circulation play a key role in redistributing heat in the world's oceans. Due to the long timescales of this circulation, ocean temperature at depth is still adjusting to effects of the Little Ice Age which occurred between the 1600 and 1800s.

Life

Life affects climate through its role in the carbon and water cycles and through such mechanisms as albedo, evapotranspiration, cloud formation, and weathering. Examples of how life may have affected past climate include:

·         glaciation 2.3 billion years ago triggered by the evolution of oxygenic photosynthesis, which depleted the atmosphere of the greenhouse gas carbon dioxide and introduced free oxygen.

·         another glaciation 300 million years ago ushered in by long-term burial of decomposition-resistant detritus of vascular land-plants (creating a carbon sink and forming coal)

·         termination of the Paleocene–Eocene Thermal Maximum 55 million years ago by flourishing marine phytoplankton

·         reversal of global warming 49 million years ago by 800,000 years of arctic azolla blooms

·         global cooling over the past 40 million years driven by the expansion of grass-grazer ecosystems

External forcing mechanisms

Human influences

In the context of climate variation, anthropogenic factors are human activities which affect the climate. The scientific consensus on climate change is "that climate is changing and that these changes are in large part caused by human activities", and it "is largely irreversible".

Of most concern in these anthropogenic factors is the increase in CO₂ levels. This is due to emissions from fossil fuel combustion, followed by aerosols (particulate matter in the atmosphere), and the CO₂ released by cement manufacture. Other factors, including land use, ozone depletion, animal husbandry (ruminant animals such as cattle produce methane, as do termites), and deforestation, are also of concern in the roles they play—both separately and in conjunction with other factors—in affecting climate, microclimate, and measures of climate variables.

Orbital variations

Slight variations in Earth's motion lead to changes in the seasonal distribution of sunlight reaching the Earth's surface and how it is distributed across the globe. There is very little change to the area-averaged annually averaged sunshine; but there can be strong changes in the geographical and seasonal distribution.

The three types of kinematic change are variations in Earth's eccentricity, changes in the tilt angle of Earth's axis of rotation, and precession of Earth's axis. Combined together, these produce Milankovitch cycles which affect climate and are notable for their correlation to glacial and interglacial periods, their correlation with the advance and retreat of the Sahara, and for their appearance in the stratigraphic record.

The IPCC notes that Milankovitch cycles drove the ice age cycles, CO₂ followed temperature change "with a lag of some hundreds of years", and that as a feedback amplified temperature change. The depths of the ocean have a lag time in changing temperature (thermal inertia on such scale). Upon seawater temperature change, the solubility of CO₂ in the oceans changed, as well as other factors affecting air-sea CO₂ exchange.

Solar output

The Sun is the predominant source of energy input to the Earth. Other sources include geothermal energy from the Earth's core, tidal energy from the Moon and heat from the decay of radioactive compounds. Both long- and short-term variations in solar intensity are known to affect global climate.

Three to four billion years ago, the Sun emitted only 75% as much power as it does today. If the atmospheric composition had been the same as today, liquid water should not have existed on Earth.

Volcanism

The eruptions considered to be large enough to affect the Earth's climate on a scale of more than 1 year are the ones that inject over 100,000 tons of SO₂ into the stratosphere. This is due to the optical properties of SO₂ and sulfate aerosols, which strongly absorb or scatter solar radiation, creating a global layer of sulfuric acid haze. On average, such eruptions occur several times per century, and cause cooling (by partially blocking the transmission of solar radiation to the Earth's surface) for a period of several years.

Volcanoes are also part of the extended carbon cycle. Over very long (geological) time periods, they release carbon dioxide from the Earth's crust and mantle, counteracting the uptake by sedimentary rocks and other geological carbon dioxide sinks.

Volcanic emissions are at a much lower level than the effects of current human activities, which generate 100–300 times the amount of carbon dioxide emitted by volcanoes. 

Arctic sea ice decline

The decline in Arctic sea ice, both in extent and thickness, over the last several decades is further evidence for rapid climate change. Sea ice is frozen seawater that floats on the ocean surface. It covers millions of square kilometers in the polar regions, varying with the seasons. In the Arctic, some sea ice remains year after year, whereas almost all Southern Ocean or Antarctic sea ice melts away and reforms annually.

Satellite observations show that Arctic sea ice is now declining at a rate of 13.2 percent per decade, relative to the 1981 to 2010 average. The 2007 Arctic summer sea ice retreat was unprecedented. Decades of shrinking and thinning in a warm climate has put the Arctic sea ice in a precarious position, it is now vulnerable to atmospheric anomalies. 

Sea level change

Recently, altimeter measurements in combination with accurately determined satellite orbits have provided an improved measurement of global sea level change. To measure sea levels prior to instrumental measurements, scientists have dated coral reefs that grow near the surface of the ocean, coastal sediments, marine terraces, ooids in lime stones, and near shore archaeological remains.

Recently, global-mean sea level rose by 195 mm during the period from 1870 to 2004. Since 2004, satellite-based records indicate that there has been a further 43 mm of global-mean sea levels rise, as of 2017.

Floods, droughts, storms

Climate change can cause an increase in precipitation, increasing the likelihood of rapid rising floods. These floods raise mortality rates by increasing drowning related deaths. Mortality rates also increase due to infectious diseases and exposure of toxic pollutants after these floods. The increase in rainfall leads to pollutants entering the water system, often contaminating drinking water with sewage, animal feces, pathogens, etc. Floods also lead to growth of fungal species and habituation of vectors of infectious diseases in previously unexposed areas, propagating the spread of vector borne diseases. Long term effects on human health are also known to be caused by flooding. Malnutrition and mental disorders, along with gastrointestinal and respiratory problems are known to increase after flooding. This most commonly occurs in less wealthy countries or areas that have more people residing in vulnerable areas and a lack of governmental aid for natural disasters and public health structures. It has been shown that the due increased precipitation from climate change, the number of people worldwide at risk of a flood would increase from 75 million to 200 million.

The changing weather patterns due to climate change cause more droughts, by decreasing levels of groundwater. The lack of groundwater leads to a decrease in health of forest trees, leading to an increase risk of wildfires. Wildfires increase the risk of physical and respiratory damage to the human body. Changing weather patterns caused by climate change can also damage crops leading to malnutrition. New wind patterns can present crops with novel pathogens and decrease the number of available pollinators which usually serve a protective role. Habitats are often affected by these changes of weather. Changes in temperature and rainfall have damaged coral reefs by introducing new pathogens and inducing physical trauma by storms. The damaged reefs increase the levels of salt that are taken up by tropical fishes eaten by locals, which may lead to adverse health outcomes.

Extreme weather

Climate change also causes more extreme weather. It is stated that climate change increases the severity of tropical storms, like Hurricane Katrina. Winter storms may become more severe because climate change increases precipitation levels and the strength of winds. Stronger storms lead to more problems with traveling and increase chances of physical trauma.

Global warming impacts on India

The latest report of the UN’s Intergovernmental Panel on Climate Change (IPCC) warns that global warming is occurring faster than anticipated and that it can have devastating impacts if steps are not taken to cut down emissions.

India will be among the worst hit countries that may face wrath of calamities like floods and heat waves, and reduced GDP.

Human activities have already raised the global temperature by one degree centigrade compared to the pre-industrial levels. The global warming is now likely to reach 1.5 degree between 2030 and 2052 if it continues to rise at the current rate, the Special Report on Global Warming of 1.5 degree C has warned.

The report has been prepared in response to an invitation from the United Nations Framework Convention on Climate Change (UNFCCC) when it adopted the Paris Agreement in 2015. The report will provide key scientific inputs to government leaders when they meet in Poland in December to review the Paris Agreement.

In terms of impacts of global warming, the report notes that the world is already witnessing the consequences of 1 degree global warming in the form of extreme weather events, rising sea levels and diminishing Arctic sea ice. There will be long-lasting or irreversible changes like the loss of some ecosystems if the temperature rises further.

South Asia, particularly India, Pakistan and China are hotspots in a warming world. All climate projections point out that these regions will be exposed to multiple and overlapping hazards at even 1.5 degree rise. The impacts will include intensified droughts and water stress, heatwaves, habitat degradation, and reduced crop yields.

“The report shows that if the global temperature increase goes up to 2 degree C instead of 1.5 degree C, the largest impact on economic growth will be (reduced GDP) on countries like India, and those in southeast Asia and Africa,”

Floods of all kinds - riverine floods, those due to snow melt and coastal flooding due to sea level rise - are increasing, and are projected to increase further. “Both the intensity and area affected by floods due to extreme rains and snow melt contribution are projected to increase over India.

More than 50 million people in India would be directly affected by sea level rise and associated coastal flooding,”

Other weather events will also change in frequency and intensity. For instance, there is an increasing frequency of cyclones over the Arabian Sea their number is a decreasing in the Bay of Bengal. However, the ratio of severe cyclones to cyclones is increasing in the Bay of Bengal. Another impact may be the shortage of fish-based protein in the Indian Ocean due to rapid degradation of key ecosystems such as coral reefs, seagrass and mangroves and factors like pollution, overfishing, unsustainable coastal development.

Extreme heatwaves too could be the new normal in India. “One of the most robust impacts is going to be related to temperature, which to a certain extent, started witnessing in India,”

“There will be manifold increase in the severe heatwave frequency and population affected in India if the global mean temperature rises to or beyond 1.5 degree by the end of the century.

The other most noticeable impacts are likely to revolve around the projected rise in mean and extreme temperature in India, which certainly will affect agriculture, water resources, energy, and public health sectors

 “whatever is the warming level, India is special. The monsoon is diminished by ice ages and global warming also has done the same. But this was most likely related to pollution (aerosols) under global warming.  So India needs to focus on improving air quality which can deliver returns in health and productivity as well as the recovery of monsoon” The efforts should include reforestation which would reduce the impact of extreme events fueled by warming of the surrounding oceans and neighbouring lands.

To limit global warming, countries will have to change policies in sectors like land, energy, industry, buildings, transport, and urban development. “Limiting global warming to 1.5 degree compared with 2 degree would reduce challenging impacts on ecosystems, human health and well-being, making it easier to achieve the United Nations Sustainable Development Goals as per IPCC Working Group III