Vital Signs of the Earth

FORCINGS: THE INITIAL DRIVERS OF CLIMATE CHANGE

1) Solar Irradiance: Solar radiation is the source of heat for planet Earth. Scientists use evidence from proxy measurements, such as sunspot counts going back centuries and ancient tree rings, to measure the amount of Sun that reaches Earth’s surface today in comparison to the past. A comprehensive study has found that the sun has an 11-year sunspot cycle, which causes about 0.1% variation in the Sun’s output. The solar cycle is incorporated into climate models.

2) Greenhouse Gas Emissions: Since the industrial revolution, concentrations of greenhouse gases such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) have risen in the atmosphere. These greenhouse gases absorb and then re-radiate heat in Earth’s atmosphere, through the above mentioned greenhouse effect, which cause increased warming.

3) Aerosols, dust, smoke, and soot: Very small airborne particles come from both human and natural sources have various effects on climate. Sulfate aerosols, which result from burning coal, biomass, and volcanic eruptions, tend to cool the earth. Other kinds of particles such as black carbon have a warming effect. The global distribution of aerosols is being tracked from the ground and from satellites.

 

CLIMATE FEEDBACKS: PROCESSES THAT EITHER AMPLIFY OR DIMINISH THE EFFECTS OF CLIMATE FORCINGS

• One feedback that increases an initial warming is a ‘positive feedback loop’.

• One feedback that reduces an initial warming is a ‘negative feedback loop’.

1) Clouds: Clouds have a huge impact on the Earth’s climate, reflecting about one-third of the total amount of sunlight that hits the Earth’s atmosphere back into space. Even small changes to the number of clouds in the sky, their location, and their type could have large consequences. A warmer climate is expected to cause more water to be held in our atmosphere, leading to an increase in cloudiness, thus altering the amount of sunlight that reaches the surface of the Earth. Less heat would get absorbed, which could slow the increased warming. This is an example of a negative feedback loop.

2) Precipitation: Global climate models show that precipitation will increase overall due to the increased amount of water held in a warmer atmosphere, but only in certain regions. Some regions will dry out instead. Regardless, changes in precipitation patterns, such as overall increased water availability, may cause an increase in plant growth on the planet as a whole, which in turn would remove more carbon dioxide from the atmosphere. If this increased water leads to more plant growth like many climate scientists predict, this would be another negative feedback loop, and would help to mitigate global warming.

3) Greening of the forests: Natural processes, such as tree growth and ocean absorption, remove about half of human CO2 emissions from the atmosphere every year. Scientists are currently studying where this CO2 goes. The delicate balance between the absorption and release of CO2 is the subject of research by many scientists. There is evidence that the ability of the oceans or forests to continue absorbing CO2 may decline as the world warms, reaching a sort of saturation point, thus leading to faster accumulation in the atmosphere. If these studies prove true, this is an example of a positive feedback loop.

Other considerations: Deforestation is a cause for concern, as there are fewer trees available to absorb CO2 from the atmosphere. Also, as the ocean absorbs CO2 from the atmosphere, it becomes more acidic. Ocean Acidification is a potentially huge issue. As the ocean becomes more acidic, marine plants and animals that use carbonate to form hard shells or other structures will suffer. These include mollusks like clams and oysters, and reef-building corals. Not only does acidification limit their access to the carbonate they need for building material, but it could also become severe enough to dissolve existing coral structures and the shells of living organisms. Coral reefs, the most biologically diverse places on the planet, are particularly vulnerable. Ocean acidification has potentially major implications for the oceans and the planet as a whole. [Source]

4) Ice Albedo: Ice is white and very reflective, in contrast to the ocean or earth’s surface, which is darker and absorbs heat faster. As the atmosphere warms, and sea and land ice melt, the darker surfaces that were once covered in ice absorb more heat. This warms the earth more, causes more ice to melt, and so on. The ice-albedo feedback is a very strong positive feedback loop. [Source]

 

CLIMATE TIPPING POINTS: WHEN EARTH’S CLIMATE ABRUPTLY MOVES BETWEEN RELATIVELY STABLE STATES

1) Ocean Circulation: As sea and land ice melt, ocean circulation is changing as a result of increased freshwater to the system. Ocean currents are a major driver of Earth’s climate and are major determiners of regional weather patterns. As more ice melts, many scientists predict ocean circulation will reach a point where currents will overturn and change drastically. This would result in major, unprecedented changes to the weather around the world, a true point of no return for our planet’s future.

2) Ice Loss: Due to the strong positive feedback loop associated with ice loss, if enough ice melts, causing Earth’s surface to absorb more and more heat, many climate scientists believe we may hit a point of no return.

3) Rapid Release of Methane: Large deposits of frozen methane, a potent greenhouse gas, and CO2 lie beneath permafrost in Arctic regions. About a quarter of the Northern Hemisphere is covered by permafrost. As the environment warms and the permafrost thaws, these deposits are predicted to release into the atmosphere and cause a major increase in global warming through the greenhouse effect.

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