Knowns and Unknowns About Climate Change

20 November 2018

A very interesting video was published yesterday (20th November 2018). This was a talk by Professor Chris Field of Stanford University given at the Stanford Energy Global Energy Forum, 1-2 November 2018. The talk – Knowns and Unknowns About Climate Change –  is an excellent summary of current thinking on climate change, its current effects and likely future developments.

Prof Field is not one to bury the lead, and starts with his overall conclusions:

  • The main known is that we need to be working harder on climate change, and
  • The main unknown is – are we going to do that?

Prof Field follows with some well known data showing the rate of increase in carbon dioxide levels in the atmosphere (a 42% rise since pre-industrial times and the highest for at least 800,000 years), and the increase in global temperatures (1.3ºC higher the pre-industrial times at a current rate of 0.2ºC increase/decade). There is now great confidence that human activities are the main cause of these increases. 

He lists some of the extreme events that occur around the world such as droughts, wild fires, coastal flooding by hurricanes, a rise in sea levels, and heavy precipitation in warmer air. He states that the warmer the Earth becomes, there is a greater risk of severe and pervasive impacts.

He then describes a number of important thresholds that we must be aware of:

Sea level increases and climate change

  • The sea level equivalent trapped in ice sheets is 18 m. Any significant melting of the ice sheets will result in a rise in sea level. The rise in sea levels in the 21st century – if we continue with high emissions – will be c.1 m, an existential situation for some countries.  If emissions are reduced then this rise will also be greatly reduced. Prof Field makes the point that this type of projection should be extended beyond the end of the 21st century to, say,  2500. The consequences of change or no change with emissions become even more stark with these longer projections. With no change in the levels of emissions the potential rise in sea level is 15 m by 2500.

Permafrost thawing

  • Permafrost thawing – As I discussed in my earlier blog (17 November 2018) the effect of significant thawing of the permafrost can have major effects.  The amount of carbon held in permafrost is four times the amount in the atmosphere. It is known that the carbon in permafrost is easily decomposable into carbon dioxide and methane if temperatures rise. The potential scale of carbon release from thawing permafrost would be self sustaining and so great that it would have a major effect on the climate even if all greenhouse gas production by humans stopped completely.  

Economic activity

  • Economic activity – Economic projections show that some economic activity is insensitive to changes in temperature but that some are affected. Basically, cooler and richer parts of the globe (e.g. Europe) might benefit economically from temperature increases, but hotter and poorer parts (South-East Asia and Sub-Saharan Africa) would suffer considerably.

The recent report of the Intergovernmental Panel on Climate Change (IPCC) describes the effect that a rise of 1.5ºC would have on the climate. At the current rate of emissions this point will be reached in just 13 years.

Prof Field completed his talk by listing some unknowns, or uncertainties, that exist in predicting the future of our climate:

  • Could be the sensitivity of the climate to greenhouse gas emissions be more sensitive than we realise, resulting in greater warming than currently predicted?
  • What about ecosystem feedback such as the thawing of the permafrost?
  • What is the sensitivity of the climate to extreme events such as wild fires?
  • What about the cascade effect where one extreme event, e.g. flooding, leads on to other effects such as a disease outbreak?
  • What level of adaption is possible where we change how we live to react to changes in the climate?
  • To what extent can we build a better world by integrating mitigation, adaptation and human development?

All together a sober and well presented argument for more activity in countering and managing climate change.