As a continuation of the articles we printed the last couple of weeks entitled Climate change controversies, Finite Planet presents this week the fifth and sixth misleading arguments in the controversy. The last four misleading arguments were:

1. Climate change not down to humans
2. ’CO2 not responsible for global warming’
3. ’rises in CO2 occur after global warming, not before’

Climate Change Controversies

Misleading argument 5: ’Global warming computer models which predict the future climate are unreliable’
“Computer models which predict the future climate are unreliable and based on a series of assumptions”
What does the science say?
Modern climate models have become increasingly accurate in reproducing how the real climate ‘works’. They are based on our understanding of basic scientific principles, observations of the climate and our understanding of how it functions.
By creating computer simulations of how different components of the climate system - clouds, the Sun, oceans, the living world, pollutants in the atmosphere and so on - behave and interact, scientists have been able to reproduce the overall course of the climate in the last century. Using this understanding of the climate system, scientists are then able to project what is likely to happen in the future, based on various assumptions about human activities.
It is important to note that computer models cannot exactly predict the future, since there are so many unknowns concerning what might happen.  Scientists model a range of future possible climates using different scenarios of what the world will ‘look like’. Each scenario makes different assumptions about important factors such as how the world’s population may increase, what policies might be introduced to deal with climate change and how much carbon dioxide and other greenhouse gases humans will pump into the atmosphere. The resulting projection of the future climate for each scenario, gives various possibilities for the temperature but within a defined range.
While climate models are now able to reproduce past and present changes in the global climate rather well, they are not, as yet, sufficiently well-developed to project accurately all the detail of the impacts we might see at regional or local levels. They do, however, give us a reliable guide to the direction of future climate change.  The reliability also continues to be improved through the use of new techniques and technologies.
Misleading argument 6: ’Global warming is all to do with the sun’
“It’s all to do with the Sun - for example, there is a strong link between increased temperatures on Earth with the number of sunspots on the Sun.”
What does the science say?
Change in solar activity is one of the many factors that influence the climate but cannot, on its own, account for all the changes in global average temperature we have seen in the 20th Century.
Changes in the Sun’s activity influence the Earth’s climate through small but significant variations in its intensity. When it is in a more active phase as indicated by a greater number of sunspots on its surface, it emits more light and heat. While there is evidence of a link between solar activity and some of the warming in the early 20th Century, measurements from satellites show that there has been very little change in underlying solar activity in the last 30 years there is even evidence of a detectable decline and so this cannot account for the recent rises we have seen in global temperatures.
The magnitude and pattern of changes to temperatures can only be understood by taking all of the relevant factors both natural and human into account. For example, major volcanic eruptions produce a cooling effect because they blast ash and other particles into the atmosphere where they persist for a few years and reduce the amount of the Sun’s energy that reaches the Earth’s surface. Also, burning fossil fuels produces particles called sulphate aerosols which tend to cool the climate in the same way.
Over the first part of the 20th Century higher levels of solar activity combined with increases in human generated carbon dioxide to raise temperatures. Between 1940 and 1970 the carbon dioxide effect was probably offset by increasing amounts of sulphate aerosols in the atmosphere, and a slight downturn in solar activity, as well as enhanced volcanic activity.
During this period global temperatures dropped. However, in the latter part of the 20th Century temperatures rose well above the levels of the 1940s. Strong measures taken to reduce sulphate pollution in some regions of the world meant that industrial aerosols began to provide less compensation for an increasing warming caused by carbon dioxide. The rising temperature during this period has been partly abated by occasional volcanic eruptions.

(to be continued next week)