Greenhouse Gases and Climate Change

Greenhouse Gases and Climate Change

Gases which trap heat in the atmosphere are called greenhouse gases. Several chemical compounds in the atmosphere act as greenhouse gases. These gases allow sunlight (shortwave radiation) to freely pass through the atmosphere and heat the land and oceans. Greenhouse gases occur naturally and allow the life to survive on Earth by warming air near the surface of the Earth.

Climate change is ‘a systematic change in the long-term state of the atmosphere over multiple decades or longer’. Statistical tests are used to determine the probability which changes in the climate are within the range of natural variability. For example, there is a less than 1 % chance that the warming of the atmosphere since 1950 could be the result of natural climate variability. At its most basic, climate change is caused by a change in the energy balance of the earth. It means that how much of the energy from the sun which enters the earth (and its atmosphere) is released back into space. The earth is gaining energy when there is a reduction in the quantity of the solar energy which is reflected out to space.

Climate change resulting from the enhanced greenhouse effect is expected to have widespread consequences, causing (i) sea-level rise and possible flooding of the low lying areas, (ii) melting of glaciers and sea ice, (iii) changes in rainfall patterns with implications for floods and droughts, and (iv) changes in the incidence of climatic extremes, especially high temperature extremes. These effects of climate change have impacts on eco-systems, health, key economic sectors such as agriculture, and water resources.

Sunlight enters the Earth’s atmosphere, passing through the greenhouse gases. As it reaches the surface of the Earth, land, water, and biosphere absorb the energy of the sunlight. Once absorbed, this energy is sent back into the atmosphere. Some of the energy passes back into space, but much of it remains trapped in the atmosphere by the greenhouse gases. This is the completely natural process and without these gases all the heat escapes back into space and average temperature of the Earth gets around 30 deg C colder. The greenhouse effect is very important process, since without it the Earth is not warm enough for the life to exist on it. But if the greenhouse effect becomes stronger, it can make the Earth warmer than normal. Even a little extra warming can cause problems for the life on the Earth.

Atmospheric scientists first used the word ‘greenhouse effect’ in the second half of 1800s. At that time, it was used to designate the naturally happening functions of trace gases in the atmosphere and did not have any negative implications. It was not up until the mid-1950s that the term greenhouse effect was attached to concern over climate alteration. And in contemporary decades, it is being frequently heard the term greenhouse effect in somewhat negative expressions. The negative concerns are related to the possible adverse impacts of the greenhouse effect.

The greenhouse effect is a natural process which is millions of years old. It was first discovered by Joseph Fourier in 1827, experimentally verified by John Tyndall in 1861, and quantified by Svante Arrhenius in 1896 who has published a paper on ’A Synopsis on the Effects of Anthropogenic Greenhouse Gases Emissions from Power Generation and Energy Consumption’. He proposed a relation between atmospheric carbon di-oxide concentrations and temperature. He and Thomas Chamberlin calculated that human activities could warm the earth by adding carbon di-oxide to the atmosphere. This was not actually verified until 1987. In 1988 it was finally acknowledged that the climate was warmer than any period since 1880.

The greenhouse effect theory was named and the Intergovernmental Panel on Climate Change (IPCC) was founded by the United Nations Environmental Programme and the World Meteorological Organization. This organization tries to predict the impact of the greenhouse effect according to existing climate models and literature information. There have been no major changes in the understanding of the greenhouse gases since ‘the 1990 Scientific Assessment for the Intergovernmental Panel on Climate Change (IPCC, 1990)’. While most of the key uncertainties identified in IPCC (1990) remain unresolved, there have been a number of important advances.

The two most abundant gases in the atmosphere, nitrogen (comprising 78 % of the dry atmosphere) and oxygen (comprising 21 %), exert almost no greenhouse effect. Instead, the greenhouse effect comes from molecules which are more complex and much less common. Water vapour is the most important greenhouse gas, and carbon di-oxide is the second most important gas. Methane, nitrous oxide, ozone and several other gases present in the atmo­sphere in small amounts also contribute to the greenhouse effect. In the humid equatorial regions, where there is so much water vapour in the air, the greenhouse effect is very large, and hence add­ing a small additional amount of carbon di-oxide or water vapour has only a small direct impact on downward infrared radiation. However, in the cold, dry Polar Regions, the effect of a small increase in carbon di-oxide or water vapour is much greater. The same is true for the cold, dry upper atmosphere where a small increase in water vapour has a greater influence on the greenhouse effect than the same change in water vapour has near the surface.

Several components of the climate system, notably the oceans and living things, affect atmospheric concentrations of green­house gases. A prime example of this is plants taking carbon di-oxide out of the atmosphere and converting it (and water) into carbo-hydrates through photo-synthesis. In the industrial era, human activities have added greenhouse gases to the atmosphere, primarily through the burning of fossil fuels and clearing of forests.

Greenhouse gases consist of three or more atoms. This molecular structure makes it possible for these gases to trap heat in the atmosphere and then transfer it to the surface of the Earth which further warms the Earth. This uninterrupted cycle of trapping heat results to an overall increase in global temperatures. The procedure, which is very similar to the way a greenhouse works, is the main reason why the gases which can produce this outcome are collectively called as greenhouse gases.

Several gases in the atmosphere can absorb heat. These greenhouse gases are produced both by natural processes and by human activities. The main greenhouse gases are carbon di-oxide (CO2), methane (CH4), nitrous oxide (N2O), and industrial gases, including hydro-fluoro-carbons, per-fluoro-carbons, and sulphur hexa-fluoride. Carbon di-oxide, methane, nitrous oxide, and certain manufactured gases called halogenated gases (gases which contain chlorine, fluorine, or bromine) become well mixed throughout the global atmosphere because of their relatively long lifetimes and because of transport by winds.

Carbon di-oxide enters the atmosphere through burning fossil fuels (coal, natural gas, and oil), solid waste, trees and other biological materials, and also as a result of certain chemical reactions (e.g., manufacture of steel and cement). Carbon di-oxide is removed from the atmosphere (or ‘sequestered’) when it is absorbed by plants as part of the biological carbon cycle.

Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from livestock and other agricultural practices, land use, and by the decay of organic waste in municipal solid waste landfills.

Nitrous oxide is emitted during agricultural, land use, industrial activities, combustion of fossil fuels and solid waste, as well as during treatment of wastewater.

Hydro-fluoro-carbons, per-fluoro-carbons, sulphur hexa-fluoride, and nitrogen tri-fluoride are synthetic, powerful greenhouse gases which are typically emitted from a variety of industrial processes. Fluorinated gases are sometimes used as substitutes for stratospheric ozone-depleting substances (e.g., chloro-fluoro-carbons, hydro-chloro-fluoro-carbons, and halons). These gases are typically emitted in smaller quantities, but since they are potent greenhouse gases, they are sometimes referred to as high ‘global warming potential’ (GWP) gases.

Water vapour is the most abundant greenhouse gas in the atmosphere and plays an important role in regulating the climate. Human activities have only direct influence on atmospheric concentrations of water vapour affecting the temperatures at the surface of the Earth primarily through irrigation and deforestation. However the quantity is small and hence it is normally not included as an indicator. The surface warming caused by human production of other greenhouse gases, however, leads to an increase in atmospheric water vapour since warmer temperatures make it easier for water to evaporate and stay in the air in vapour form. This creates a positive ‘feedback loop. in which warming leads to more warming.

Ozone is also a greenhouse gas, but it differs from other greenhouse gases in several ways. The effects of ozone depend on its altitude, or where the gas is located vertically in the atmosphere. Majority of ozone naturally exists in the layer of the atmosphere called the stratosphere, which ranges from around 10 kilometers to 30 kilometers above the surface of the Earth. Ozone in the stratosphere has a slight net warming effect on the Earth, but it is good for life on the Earth since it absorbs harmful ultraviolet radiation from the Sun, preventing it from reaching the surface of the Earth. In the troposphere (the layer of the atmosphere near the ground level) ozone is an air pollutant which is harmful to breathe, a main ingredient of urban smog, and an important greenhouse gas which contributes to climate change. Unlike the other major greenhouse gases, tropospheric ozone only lasts for days to weeks, so levels frequently vary by location and by season.

Since the Industrial Revolution began in the 1700s, people have added a substantial quantity of greenhouse gases into the atmosphere by burning fossil fuels, cutting down forests, and conducting other activities. When greenhouse gases are emitted into the atmosphere, many remain there for long time periods ranging from a decade to many millennia. Over time, these gases are removed from the atmosphere by chemical reactions or by emissions sinks, such as the oceans and vegetation, which absorb greenhouse gases from the atmosphere. As a result of human activities, however, these gases are entering the atmosphere more quickly than they are being removed, and hence their concentrations are increasing. Human activities are now increasing the quantity of greenhouse gases in the atmosphere, which is leading to changes in the climate.

The Sun powers the climate of the Earth by radiating energy at very short wavelengths, predominately in the visible or near-visible (e.g. ul­traviolet) part of the spectrum. Roughly one-third of the solar energy which reaches the top of the atmosphere of the Earth, is reflected di­rectly back to space. The remaining two-third is absorbed by the surface and, to a lesser extent, by the atmosphere. To balance the absorbed incoming energy, the Earth, on an average, is required to radiate the same amount of energy back to space. Since the Earth is much colder than the Sun, it radiates at much longer wavelengths, pri­marily in the infrared part of the spectrum. Much of this thermal radiation emitted by the land and ocean is ab­sorbed by the atmosphere, including clouds, and re-radiated back to Earth. This is called the greenhouse effect.

The greenhouse effect is a foremost factor in keeping the Earth comfortable to live, since it keeps some of the heat of the Earth which otherwise would escape from the atmosphere out to space. In fact, without the greenhouse effect the average global temperature of the Earth would be much colder and life on Earth as we recognize it would not be possible.

The glass walls in a greenhouse reduce airflow and increase the temperature of the air inside. Analogously, but through a different physical process, the greenhouse effect of the Earth is there. It warms the surface of the Earth. Greenhouse effect is naturally occurring and keeps the surface of the Earth warm. It is vital to the survival of life on Earth. Without the greenhouse effect, the average surface temperature of the Earth is likely to be below the freezing point of water. Hence, the natural greenhouse effect of the Earth makes the life on the Earth pos­sible.

The Earth becomes warmer with more heat trapped on the Earth. This means the weather all over Earth changes. Since the conditions are perfect for existence of life on Earth, a large rise in temperature can be disastrous for the life on Earth. At the moment, it is difficult for the environment scientists to say how big the changes are going to be and where the worst effects are going to occur. Fig 1 shows the idealized model of the natural greenhouse effect.

Fig 1 Idealized model of the natural greenhouse effect

Adding more of a greenhouse gas, such as carbon di-oxide, to the at­mosphere intensifies the greenhouse effect, hence warming the climate of the Earth. The quantity of warming depends on various feedback mechanisms. For example, as the atmosphere warms due to rising levels of greenhouse gases, its concentration of water vapour increases, further intensifying the greenhouse effect. This in turn causes more warming, which causes an additional increase in water vapour, in a self-reinforcing cycle. This water vapour feed­back can be strong enough to approximately double the increase in the greenhouse effect due to the added carbon di-oxide alone.

Additional important feedback mechanisms involve clouds. Clouds are effective at absorbing infrared radiation and hence exert a large greenhouse effect, hence warming the Earth. Clouds are also effective at reflecting away incoming solar radiation, hence cooling the Earth. A change in almost any aspect of clouds, such as their type, location, water content, cloud altitude, particle size and shape, or lifetimes, affects the degree to which the clouds warm or cool the Earth. Some changes amplify warming while others diminish it.

Greenhouse gases vary in their ability to absorb and hold heat in the atmosphere. Hydro-fluoro-carbons and per-fluoro-carbons are the most heat absorbent gases, but there are also wide differences between naturally occurring gases. For example, nitrous oxide absorbs 265 times more heat per molecule than carbon di-oxide, and methane absorbs 25 times more heat per molecule than carbon di-oxide. However, carbon di-oxide contributes the most, since its level in the atmosphere is the highest. The effect of each gas on the climate change depends on three main factors namely (i) concentration or abundance, (ii) stay in the atmosphere, and (iii) impact on the atmosphere. Tab 1 gives effect of some of the greenhouse gases on global warming.

Tab 1 Effect of greenhouse gases on global warming
Greenhouse gasChemical formulaGlobal Warming Potential, 100-year time horizonAtmospheric Lifetime (years)
Carbon di-oxideCO21100
Nitrous oxideN2O265121
Chloro-fluoro-carbon-12         (CFC-12)CCl2F210,200100
Hydro-fluoro- carbon-23           (HFC-23)CHF312,400222
Sulphur hexa-fluorideSF623,5003,200
Nitrogen tri-fluorideNF316,100500
Note:  No single lifetime can be given for carbon di-oxide since it moves throughout the Earth system at differing rates. Some carbon di-oxide is absorbed very quickly, while some remain in the atmosphere for thousands of years.

 Concentration, or abundance, is the quantity of a particular greenhouse gas in the air. Larger emissions of greenhouse gases lead to higher concentrations in the atmosphere. Concentrations of the greenhouse gases are measured by volume in parts per million (ppm), parts per billion (ppb), and even parts per trillion (ppt). In other words, a concentration of 1 ppb for a given gas means there is one molecule of the gas in every 1 billion molecules of air. One part per million is equivalent to one drop of water diluted into around 49 litres of liquid. Some halogenated gases are considered major greenhouse gases due to their very high global warming potentials and long atmospheric lifetimes even if they only exist at a few ppt

Each of the greenhouse gases can remain in the atmosphere for different quantities of time, ranging from a few years to thousands of years. All of these gases remain in the atmosphere long enough to become well mixed, meaning that the quantity which is measured in the atmosphere is roughly the same all over the world, regardless of the source of the emissions.

Greenhouse gases impact the atmosphere of the Earth. Some gases are more effective than others at making the Earth warmer and ‘thickening the blanket of the Earth’. For each greenhouse gas, a GWP has been calculated to reflect how long it remains in the atmosphere, on average, and how strongly it absorbs energy. Gases with a higher GWP absorb more energy, per kilogram, than the gases with a lower GWP, and hence contribute more to warming the Earth.

Climate forcing

When energy from the Sun reaches the Earth, Earth absorbs some of this energy and radiates the rest back to space as heat. The surface temperature of the Earth depends on this balance between incoming and outgoing energy. Average conditions tend to remain stable unless the Earth experiences a force which shifts the energy balance. A shift in the energy balance causes the average temperature of the Earth to become warmer or cooler, leading to a variety of other changes in the lower atmosphere, on land, and in the oceans.

A variety of physical and chemical changes can affect the global energy balance and force changes in the climate of the Earth. Some of these changes are natural, while others are influenced by humans. These changes are measured by the quantity of warming or cooling they can produce, which is called ‘radiative forcing’. Changes which have a warming effect are called ‘positive’ forcing, while changes which have a cooling effect are called ‘negative’ forcing. When positive and negative forces are out of balance, the result is a change in the average surface temperature of the Earth.

Roughly half of the carbon di-oxide emitted by human activities today remains in the atmosphere. The rest is absorbed by oceans and land eco-systems. The fraction of emissions remaining in the atmosphere, called airborne fraction, is an important indicator of the balance between sources and sinks. Airborne fraction varies a lot from year to year, and over the past 60 years the relatively uncertain annual averages have varied between 0.2 (20 %) and 0.8 (80 %). However, statistical analysis shows that there is no significant trend in the average airborne fraction value of 0.42 over the long term (around 60 years). This means that only 42 % of human carbon di-oxide emissions remain in the atmosphere. Land and ocean carbon di-oxide sinks have continued to increase proportionally with the increasing emissions. It is uncertain how airborne fraction is going to change in the future since the uptake processes are sensitive to climate and land-use changes.

Globally averaged surface mole fractions for carbon di-oxide, methane and nitrous oxide reached new highs in 2020, with carbon di-oxide at 413.2 +/- 0.2 ppm, methane at 1889 +/- 2 ppb and nitrous oxide at 333.2 +/- 0.1 ppb. These values constitute, respectively, 149 %, 262 % and 123 % of pre-industrial (before 1750) levels.

Carbon di-oxide is the single most important anthropogenic greenhouse gas in the atmosphere, accounting for around 66 % of the radiative forcing by the long lived greenhouse gases. It is responsible for around 82 % of the increase in radiative forcing over the past decade and also around 82 % of the increase over the five years since 2015. The pre-industrial level of 278 ppm represented a balance of fluxes among the atmosphere, the oceans and the land biosphere.

Methane accounts for about 16 % of the radiative forcing by the long lived greenhouse gases. Around 40 % of methane is emitted into the atmosphere by natural sources (for example, wetlands and termites), and around 60 % comes from anthropogenic sources (for example, ruminants, rice agriculture, fossil fuel exploitation, landfills and biomass burning).

Nitrous oxide accounts for around 7 % of the radiative forcing by the long lived greenhouse gases. It is the third most important individual contributor to the combined forcing. It is emitted into the atmosphere from both natural sources (around 60 %) and anthropogenic sources (around 40 %), including oceans, soils, biomass burning, fertilizer use and various industrial processes.

The stratospheric ozone-depleting CFCs, which are regulated by the ‘Montreal Protocol on Substances that Deplete the Ozone Layer’, together with minor halogenated gases, account for around 11 % of the radiative forcing by the long lived greenhouse gases. While the chloro-fluoro-carbons and most halons are decreasing, some hydro-chloro-fluoro-carbon and hydro-fluoro-carbons, which are also potent greenhouse gases, are increasing at relatively rapid rates, although they are still low in abundance (at ppt) levels. Fig 2 shows contribution of greenhouse gases in global warming and carbon di-oxide mole fraction.

Fig 2 Contribution of greenhouse gases in global warming and carbon di-oxide mole fraction

Fig 3 shows the relative forcing caused by major long lived greenhouse gases (carbon di-oxide, methane, and nitrous oxide) together with di-chloro-difluoro-methane (CFC-12) and tri-chloro-fluoro-methane (CFC-11) since 1980. These gases account for around 96 % of radiative forcing due to the long lived greenhouse gases. It shows the quantity of radiative forcing based on the change in concentration of these gases in the atmosphere of the Earth. All percentage contributions to radiative forcing are calculated using 1750 as a reference period. Radiative forcing is calculated in watts per square meter, which represents the size of the energy imbalance in the atmosphere. On the right side of the graph, radiative forcing has been converted to the ‘annual greenhouse gas index’, which is set to a value of 1.0 for 1990.

Fig 3 Relative forcing caused by major long lived greenhouse gases

Changes in greenhouse gas concentrations in the atmosphere affect radiative forcing. Greenhouse gases absorb energy which radiates upward from the surface of the Earth, re-emitting heat to the lower atmosphere and warming the surface of the Earth. Human activities have led to increased concentrations of greenhouse gases which can remain in the atmosphere for decades, centuries, or longer, so the corresponding warming effects is going to last for a long time.

Greenhouse gases produced by human activities have caused an overall warming influence on the climate of the Earth since 1750. The largest contributor to warming has been carbon di-oxide, followed by methane and black carbon. Although aerosol pollution and certain other activities have caused cooling, the net result is that human activities on the whole have warmed the Earth. Fig 4 shows the radiative forcing caused by human activities since 1750.

Fig 4 Radiative forcing caused by human activities since 1750

Climate change

Since 1900, the global average surface temperature has increased by around 1 deg C. This has been accompanied by warming of the ocean, a rise in sea level, a strong decline in Arctic sea ice, widespread increases in the frequency and intensity of heat waves, and several other associated climate effects. Much of this warming has occurred in the last five decades. Detailed analyses have shown that the warming during this period is mainly a result of the increased concentrations of carbon di-oxide and other greenhouse gases. Continued emissions of these gases is causing further climate change, including substantial increases in global average surface temperature and important changes in regional climate. The magnitude and timing of these changes depends on several factors, and slow-downs and accelerations in warming lasting a decade or more is going to continue to occur. However, long term climate change over several decades depends mainly on the total quantity of the carbon di-oxide and other greenhouse gases emitted as a result of human activities.

There are multiple lines of evidence which show the change in the climate system. Several countries are already experiencing the impacts of the changing climate; particularly changes associated with increases in temperature, frequency, and intensity of heat-waves, hazardous fire weather, and drought conditions. Climate observations and future projections show that these changes from the historical climate are ongoing and long-term, and that they cannot be explained by natural variability (though they do interact with underlying natural variability). Fig 5 gives evidences showing climate change.

Fig 5 Evidences showing climate change

Climate change is causing the following five critical global environmental changes.

  • Climate change is warming temperature of the surface and the oceans of the Earth. The Earth has warmed at a rate of 0.13 deg C per decade since 1957, almost twice as fast as its rate of warming during the previous century.
  • Climate change is causing changes in the global water cycle (‘hydrologic’ cycle): Over the past century there have been distinct geographical changes in total annual precipitation, with some areas experiencing severe and long-term drought and others experiencing increased annual precipitation. Frequency and intensity of storms increases as the atmosphere warms and is able to hold more water vapour.
  • Climate change is reducing glaciers and snowpack. Across the globe, nearly all glaciers are decreasing in area, volume, and mass. One billion people living in river watersheds fed by glaciers and snowmelt are thus impacted.
  • Climate change is causing rise in sea level. Warmer water expands, so as oceans warm the increased volume of water is causing sea level rise. Melting glaciers and snowpack also contribute to the rising level of the seas.
  • Climate change is causing ocean acidification. Oceans absorb around 25 % of the emitted carbon di-oxide from the atmosphere, leading to acidification of seawater.

The above global changes result in what is being experienced as the changes in the local weather and climate such as (i) higher variability, with ‘wetter wets’, ‘drier dries’ and ‘hotter hots’, (ii) more frequent and severe extreme heat events, (ii) more severe droughts, (v) more intense precipitation, such as severe rains, storms, cyclones, and hurricanes, (vi) higher average temperatures and longer frost-free seasons, (vii) longer wildfire seasons and worse wildfires, (viii) loss of snowpack and earlier spring runoff, (ix) recurrent coastal flooding with high tides and storm surges, (x) more frequent and severe floods due to intense precipitation and spring snowmelt, (xi) worsening air quality since higher temperatures increase production of ozone (a key contributor to smog) and pollen, as well as increasing the risk of wildfires, and (xii) longer pollen seasons and more pollen production. In turn these regional and local climatic changes result in the environmental, social, and economic changes which are associated with human health impacts.

In general, climate solutions fall into two big buckets namely (i) mitigation, and (ii) adaptation. Increasingly, government authorities and community organizations also talk about measures to increase climate ‘resilience’. These concepts are not distinct, and are all inter-related. Mitigation refers to the measures to reduce the quantity and speed of future climate change by reducing emissions of heat-trapping gases or removing carbon di-oxide from the atmosphere. Adaptation refers to the measures taken to reduce the harmful impacts of climate change or take advantage of any beneficial opportunities through ‘adjustments in natural or human systems’. Resilience means the capability to anticipate, prepare for, respond to, and recover from significant threats with minimum damage to social well-being, the economy, and the environment.

Mitigation – Mitigation is essential since scientists agree that the higher is the rise in the global temperature, the greater is the adverse consequences of climate change. Also, if emissions are unchecked, there is a higher danger of abrupt climate change or surpassing ‘tipping points’. For example, collapse of the West Antarctic ice sheet can lead t very rapid sea level rise, or melting of permafrost can lead to large releases of methane which further increases warming through a positive feedback loop. Catastrophic climate change can surpass the capacity to adapt. For example, a recent study suggests that heat levels in parts of the Middle East can exceed the body’s survival threshold unless the greenhouse gas emissions levels are quickly reduced.

There are many mitigation strategies which offer feasible and cost-effective ways to reduce greenhouse gas emissions. These include the use of clean and renewable energy for electricity production, walking, biking, and using low carbon or zero emission vehicles, reducing meat consumption, less flying, changing agricultural practices, limiting deforestation, and planting trees.

Adaptation – Adaptation strategies are needed to reduce the harmful impacts of climate change and allow communities to thrive in the face of climate change. The impacts of climate change are already evident in extreme weather, more explosive wildfires, higher temperatures, and changes in the distribution of disease-carrying vectors. Since greenhouse gases persist in the atmosphere for a long time, more serious climate impacts are to be experienced even if the emissions of all the greenhouse gasses are stopped today.

Cool roofs, planting trees, and air conditioning are all effective adaptation strategies to reduce the impacts of rising temperatures and more frequent heat waves. Seawalls and restoration of wetlands are both strategies to address sea level rise. Emergency preparedness planning which takes climate changes into account is one way to adapt to the increased frequency of climate resilience. It is essential to increase the capacity to anticipate, plan for, and reduce the dangers of the environmental and social changes brought about by climate change, and to seize any opportunities associated with these changes.

Climate vulnerability and climate resilience – Climate vulnerability is the degree to which people or communities are at risk of experiencing the negative impacts of climate change. The flip side of climate vulnerability is climate resilience, which is the capacity to anticipate, plan for, and reduce the dangers of the environmental and social changes brought about by the climate change, and to seize any opportunities associated with these changes. Since several communities presently lack the power, resources, and opportunities which promote health and economic well-being, the concept of resilience also implies promoting the ability to not just remain the same in the face of climate change or after an extreme event, but also to become stronger and healthier,  that is, to ‘bounce forward’. Geographical location is, of course, an important consideration in climate vulnerability. Low-lying coastal communities are clearly at higher risk of coastal flooding from sea level rise and tidal storm surges than communities at higher altitudes. Three additional factors are most significant in determining the level of climate vulnerability or resilience in individuals and communities. These three factors are (i) pre-existing health status, (ii) living and working conditions, and (iii) lack of power and voice.


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