Connecting, Nurturing, Creating for Sustainable Environment

Understanding Climate Change

Understanding Climate Change


The Science: What is Climate Change?
Definitions of climate change:
The Intergovernmental Panel on Climate Change (IPCC)defines climate change as ‘any change in climate over time, whether due to natural variability or as a result of human activity'.
The United Nations Framework Convention on Climate Change (UNFCCC) defines climate change as ‘a change of climate that is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and that is in addition to natural climate variability observed over comparable time periods’. In other words, the UNFCCC uses the term climate change to mean only those changes that are brought about by human induced changes in green house gases (GHGs).
The World Meteorological Organisation (WMO) defines climate change as ‘a statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer). Climate change may be due to natural internal processes or external forcing, or to persistent anthropogenic changes in the composition of the atmosphere or in land use’.
The Intergovernmental Panel on Climate Change (IPCC) concluded in its Synthesis Report 2007, "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic (man-made) greenhouse gas concentrations" via the greenhouse effect.
The greenhouse effect causes the atmosphere to trap more heat energy at the Earth's surface and within the atmosphere by absorbing and re-emitting longwave energy. It is a naturally occurring process that results from the fact that certain atmospheric gases, such as carbon dioxide, water vapor, and methane, are able to change the energy balance of the planet by absorbing longwave radiation emitted from the Earth's surface. Without the greenhouse effect life on this planet would probably not exist as the average temperature of the Earth would be a chilly -18° Celsius, rather than the present 15° Celsius.
Since the Industrial Revolution, mankind has been releasing extra quantities of greenhouse gases into the atmosphere, which trap more heat, enhancing the natural greenhouse effect. This is known as the "enhanced" greenhouse effect and is the direct result of human activities. Processes such as the burning of fossil fuels, industrial operations and forest clearing release have increased the amount of carbon dioxide entering the atmosphere.

Carbon Dioxide is the Main Culprit
Emissions from fossil fuel combustion account for about 65% of the extra carbon dioxide now found in our atmosphere. The remaining 35% is derived from deforestation and the conversion of prairie, woodland, and forested ecosystems primarily into agricultural systems. Natural ecosystems can hold 20 to 100 times more carbon dioxide per unit area than agricultural systems.
Average concentrations of atmospheric carbon dioxide in the year 2007 were about 384 parts per million. Prior to 1832, ice core levels of carbon dioxide were about 284 parts per million. Today, we are at 100 ppm (35%) above the 1832 ice core levels of 284 ppm.
Every time we put on the air-con, turn on a light, use a computer, drive our car, watch television or boil the kettle, we are creating carbon dioxide (CO2) . Carbon dioxide has an atmospheric lifetime of between 50 and 200 years. This means that carbon dioxide will be present in the atmosphere for at least 50 years before it is absorbed by a sink or becomes part of another chemical reaction. Consequently, carbon dioxide emitted into the atmosphere today could cause global warming for up to two centuries.
Your cup of tea lasts a very long time!
Methane is Also a Worry
Since 1750, methane (CH4) has doubled, and could double again by 2050. Each year we add 350-500 million tons of methane to the air by raising livestock, coal mining, drilling for oil and natural gas, rice cultivation, and garbage sitting in landfills. It stays in the atmosphere for only 10 years, but traps 20 times more heat than carbon dioxide.


How Exactly has our Climate Changed?
The Fifth Assessment Report (AR 5) created by the IPCC was finalized in 2014. It considered the new evidence of climate change based on independent scientific analysis from observations of the climate system, archives and climate models.

It has the strongest statement so far regarding the impact of human activities on observed warming and the increase in global average temperatures.

Findings of Intergovernmental Panel on Climate Change Fifth Assessment Report

1.     “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.”

2.     “Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history. The atmospheric concentration of key greenhouse gases — carbon dioxide, methane, and nitrous oxide — is “unprecedented in at least the last 800,000 years,” the report warns, and our fossil-fuel driven economies and ever-increasing population are to blame.”

3.     “Greenhouse gases contributed a global mean surface warming likely to be in the range of 0.5°C to 1.3°C over the period 1951 to 2010, with the contributions from other anthropogenic forcings, including the cooling effect of aerosols, likely to be in the range of −0.6°C to 0.1°C. The contribution from natural forcings was likely to be in the range of −0.1°C to 0.1°C, and from natural internal variability was likely to be in the range of −0.1°C to 0.1°C. Together these assessed contributions are consistent with the observed warming of approximately 0.6°C to 0.7°C over this period.”

4.     “Heat waves will occur more often and last longer … extreme precipitation events will become more intense and frequent in many regions. The ocean will continue to warm and acidify, and global mean sea level will continue to rise,” the report states. If we stick to our current path, we could see 3.7 to 4.8 degrees Celsius of warming — or even more — by the end of the century.”

5.     “Ocean warming dominates the increase in energy stored in the climate system, accounting for more than 90% of the energy accumulated between 1971 and 2010 (high confidence). It is virtually certain that the upper ocean (0−700 m) warmed from 1971 to 2010 and it likely warmed between the 1870s and 1971.”

6.     “Over the last two decades, the Greenland and Antarctic ice sheets have been losing mass, glaciers have continued to shrink almost worldwide, and Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent (high confidence)”

7.     “The rate of sea level rise since the mid-19th century has been larger than the mean rate during the previous two millennia (high confidence). Over the period 1901 to 2010, global mean sea level rose by 0.19 [0.17 to 0.21] m”


Representative Concentration Pathways from AR 5


Key characteristics of the scenarios from AR 5 (Source: Climate Change 2014 Synthesis Report, Summary for Policy Makers,




Impact of Climate Change on Financial Institutions

(source: Climate change: Implications or Investors and Financial Institutions)

1.     Climate change will apply differentially to all sectors of the economy.

2.     To meet the target of keeping warming to less than 2o Celsius from pre-industrial levels, investment patterns will need to divest from fossil fuel extraction and fossil-fuel based power generation and will have to invest in low-carbon energy and energy efficiency.

3.     Climate change and extreme weather events will affect agriculture, infrastructure and precipitation in ways that have not yet been completely understood.

4.     Society’s response to climate change will depend on the decisions made by private sector investors and financial institutions.

5.     For the aforementioned investment, capital will be required, majority of which the government will turn to the private sector to provide.



Future based on the policy adopted to cut carbon emissions. (Source: Climate Change: Action, Trends and Implications for Business, University of Cambridge)




Tipping Points

A tipping point is a critical threshold where the future state of the system can be qualitatively altered by a small change in forcing. A tipping element is a part of the Earth system that has a tipping point. Tipping elements that can be forced past a tipping point this century by human activities are relevant to policy makers. The following is a diagrammatic representation of tipping elements that are relevant to policy.


(source: Earth System Tipping Points, University of East Anglia)



Stern Review

The Stern Review was published in 2006 and provided overwhelming scientific evidence to take action to stabilize greenhouse gases. It presented the need to work together to tackle climate change and represented an important stepping stone towards responding to climate change.

The forecasts for the economic cost of climate change in Sir Nicholas Stern’s review are based on stabilising emissions at 550 parts per million in the atmosphere of CO2 and its equivalent gases (ppm CO2e). A doubling of CO2 over pre-industrial levels carries an extremely high risk of exceeding 2°C of global warming. Throughout the review, Stern considers the implications of stabilizing within a range between 450 and 550ppm CO2e. Even at 450ppm stabilisation, there is a greater than 50% of exceeding 2°C.


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