How do we know what we know about climate change? Five key undisputed points about global warming.

Posted by sustainable on June 1, 2012 Blog Add comments

There has been much discussion about whether global warming is caused by human activity and whether it will lead to global warming. However, there are a number of undisputed points that society has learnt from science that lead to clear conclusions that global warming is caused by human activity. These key points are the culmination of over 150 years of learning that has resulted in questions about the sustainability of human society. Individually, the points don’t tell us much about sustainability. But together, they provide a clear and succinct ‘story’ that leads to clear conclusions. This story can be used to explain to others how we know what we know about climate change. They also highlight the importance of science for enhancing sustainable learning.

The Five Points of Global Warming:

  1. Observations show that the level of carbon dioxide is increasing in the atmosphere. Direct observations since the 1950s clearly show the yearly increase in carbon dioxide.
  2. We know that this rise in atmospheric carbon dioxide is due to the burning of fossil fuels and not volcanoes. Carbon dioxide comes in two ‘flavors’ based on the two stable carbon atoms, Carbon-12 and Carbon-13. Fossil fuels are rich in Carbon-12. When we burn fossil fuels we put more Carbon-12 in the atmosphere relative to Carbon-13, which is precisely what is observed in the  record of increasing carbon dioxide in the Earth’s atmosphere.
  3. Carbon dioxide is a gas that is very efficient at producing a greenhouse effect. This has been known for over 150 years. In 1859 John Tyndall carried out laboratory experiments where he placed different gases in a container and measured how these individual gases absorbed heat radiation (longwave radiation). He found that carbon dioxide is a very efficient greenhouse gas compared to other gases.
  4. Thus, increasing atmospheric carbon dioxide will increase the greenhouse effect of Earth. Increasing carbon dioxide traps more heat radiation leaving Earth’s surface, which is called the greenhouse effect.
  5. The Earth’s surface must warm from this increase in the greenhouse effect. This is a result of the first law of thermodynamics, which is an expression of the conversation of energy. The first law of thermodynamics is an undisputed law that was first formulated in 1850 by Rudolf Clausius. The trapped energy (heat radiation) must result in a warming of Earth’s surface as it has nowhere else to go.

These five points of global warming are validated by observations of Earth’s deep past. Millions of years ago Earth’s atmospheric carbon dioxide levels were higher than today. The past increase in carbon dioxide was due to the very slow build-up of carbon dioxide over hundreds of thousands to millions of years from volcanic activity, as compared to the very rapid build-up today due to the burning of fossil fuels. Observations show that when atmospheric carbon dioxide was higher in the past, Earth was warmer.

This is important for understanding where we are heading in the future. For if we continue to burn fossil fuels at their current rate, then atmospheric carbon dioxide levels will be 800 to 1100 parts per million in concentration by 2100 compared to 396 parts per million now. The last time there was that much carbon dioxide in the atmosphere was 30 to 40 million years ago. At that time Earth was very warm and there was little evidence of glacier formations on either Greenland or Antarctica and much higher sea levels.

All of the points made above are based on direct observations and the fundamental law of conservation of energy. They are not dependent on the results of climate models. However, results from climate models are in agreement with these observed facts. Overall, the points highlight that continued release of carbon dioxide as a result of human activity will inevitably result in global warming and there is evidence from scientific studies that this is already occurring.

Jeffrey T. Kiehl is a senior scientist at the National Center for Atmospheric Research in Boulder, Colorado, USA. He is the head of the Climate Change Research Section and has carried out research on Earth’s past, present and future climates for over 30 years.