climate change | a little introduction

A polar bear onto cracking ice
Polar bears are facing rapid loss of the sea ice where they hunt and breed.

Climate change is a big topic and giving a thoroughly and complete explanation is really a big challenge. Let`s start with answering a few questions.

Please fill free to comment on this post and on the ones that will follow, to add your own questions, to propose answers, and to suggest different views. I`d really like to create an open and valuable conversation around the issue of climate change.
We have many scientists and experts on climate change @DMU that will be happy to help with your doubts and questions.

What is climate change?
In the most general sense, the term “climate change” encompasses all forms of climatic inconstancy (that is, any differences between long-term statistics of the meteorological elements calculated for different time period but relating to the same geographical area) regardless of their natural or physical causes. Climate change may result from different factors such as changes in solar activity, long-period changes in the Earth’s orbital elements, natural internal processes of the climate system, or anthropogenic forcing (for example, human activities that increase the atmospheric concentrations of carbon dioxide and other greenhouse gases).

Schematic view of the components of the climate system, their processes and interactions.
Source co2now.org

However, the term “climate change” is often used in a more restricted sense, to denote a significant change (such as a change having important economic, environmental and social effects) in the mean values of a meteorological element (in particular temperature or amount of precipitation) in the course of a certain period of time, where the means are taken over periods of the order of a decade or longer.

Is the Earth climate really changing?
There is agreement among the scientific community that the earth has warmed in the last century. A joint statement signed by the heads of the national science academies in Brazil, Canada, China, France, Germany, India, Italy, Japan, Russia, the UK, and the US states that:
Climate change is real. There will always be uncertainty in understanding a system as complex as the world’s climate. However there is now strong evidence that significant global warming is occurring. The evidence comes from direct measurements of rising surface air temperatures and subsurface ocean temperatures and from phenomena such as increases in average global sea levels, retreating glaciers, and changes to many physical and biological systems.
The IPCC, a UN scientific body convened to assess science relating to climate change, stated in its last assessment that “warming of the climate system is unequivocal”. The same report – drawing on the full range of published science papers on the subject – points to a rise of about three-quarters of a degree Celsius in the past century, with much of that warming taking place over the past few decades.
Of course, the fact that the world is warming doesn’t mean that it is getting hotter in a uniform way. The long-term rise in temperature is affected by shorter term factors such as changes in solar activity and regional cycles. And some regions – such as the Arctic – are warming significantly faster than others.

What are the observed changes in the planet climate?

  • All data sets of surface temperature measurements over the land and oceans show quite similar upward trends globally, with two major warming periods globally: 1910 to 1945 and since 1976.
Global land-ocean temperature index
Source climate.nasa.gov

The video shows the differences between the measured temperatures and the mean of hystoric temperatures.  Colour varies form dark blue, that means a negative difference of 2 degrees, white that means no difference, and red that is a positive difference of 2 degree. 
 
  • The decrease in the continental diurnal temperature range coincides with increases in cloud amount, precipitation, and increases in total water vapour.
  • The nearly worldwide decrease in mountain glacier extent and ice mass is consistent with worldwide surface temperature increases. A few recent exceptions in coastal regions are consistent with atmospheric circulation variations and related precipitation increases.The systematic decrease in spring and summer sea-ice extent and thickness in the Arctic is consistent with increases in temperature over most of the adjacent land and ocean.
Land ice extention variation over Antarctica and Greenland
Source climate.nasa.gov
Artic sea ice extent
Source climate.nasa.gov
  • Sea level rose about 17 centimetres in the last century. The rate in the last decade, however, is nearly double that of the last century.  Sea level rise is caused by the expansion of sea water as it warms up in response to climate change and the widespread melting of land ice.
Sea level rise from 1870
Source climate.nasa.gov
  • The increases in total tropospheric water vapour (troposphere is the lowest portion of atmosphere) in the last 25 years are consistent with increases in tropospheric temperatures and an enhanced hydrologic cycle, resulting in more extreme and heavier precipitation events in many areas with increasing precipitation.
  • Ocean acidification. Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30 percent. This increase is the result of humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the oceans. The amount of carbon dioxide absorbed by the upper layer of the oceans is increasing by about 2 billion tonnes per year.

[Houghton, Ding, et al. 2001]

Are humans definitely causing climate change?
There is strong evidence that the warming of the Earth over the last half-century has been caused largely by human activity, such as the burning of fossil fuels and changes in land use, including agriculture and deforestation [Pethica 2010]. The human-induced climate-change is argued in three steps: (1) human fossil fuel burning causes carbon dioxide concentrations to rise; (2) carbon dioxide is a greenhouse gas; (3) increasing the greenhouse effect increases average global temperatures (and has many other effects) [MacKay 2009].
Human activities contribute to climate change by causing changes in the amounts of greenhouse gases, aerosols (small particles), and cloudiness in Earth’s atmosphere. The largest known contribution comes from the burning of fossil fuels, which releases carbon dioxide gas to the atmosphere. Greenhouse gases and aerosols affect climate by altering incoming solar radiation and out- going infrared (thermal) radiation that are part of Earth’s energy balance. Changing the atmospheric abundance or properties of these gases and particles can lead to a warming or cooling of the climate system. Since the start of the industrial era (about 1750), the overall effect of human activities on climate has been a warming influence. The human impact on climate during this era greatly exceeds that due to known changes in natural processes, such as solar changes and volcanic eruptions [IPCC 2007].

So, what do you think about climate change? Do you agree or you don`t that the planet`s climate is changing?

To what extent do you think climate change is a result of human behaviour or natural changes?

How concerned are you about the effects on the environment of climate change, if at all?

More about the topic will follow during this week. But please feel free to ask me what you would like to know!

References:
The following list doesn`t intend to be complete or exhaustive, but to give you a place to start. Please share with us any literature you think is important to understand and make sense of climate change.
Oliver, C., G. Frigeri, et al. (2011). “Everything you need to know about climate change – interactive.”
DEFRA (2010). Defra`s Climate Change Plan 2010. London, Department for Environment Food and Rural Affairs.
Pethica, J. (2010). Climate change: a summary of the science. London, The Royal Society.
MacKay, d. J. (2009). Sustainable Energy – Whithout the hot air. Cambridge, England, UIT.
IPCC (2007). Climate Change 2007: The Physical Science Basis. S. Solomon, D. Qin, M. Manninget al. Cambridge, United Kingdom and New York, USA, Intergovernmental Panel on Climate Change.
Houghton, J. T., Y. Ding, et al. (2001). Climate change 2001: the scientific basis. New York, Cambridge University Press.
RCEP (2000). 22nd Report. Energy – The changing climate. London, Royal Commision on Environmental Pollution.

Links:
the carbon trust
department for environment food and rural affairs [DEFRA]
department of energy and climate change [DECC]
people and the planet

the nasa website for climate change

frequently asked questions
climate change myths and fact

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