# We Answer Your Questions about Global Warming

Some erroneous descriptions have given rise to the recent controversy over the credibility of the IPCC Fourth Assessment Report (AR4).

However, these errors concern only a small portion of the AR4 that runs about 1,000 pages and the credibility of the AR4's scientific basis regarding global warming remains intact. Following the recent controversy, the IPCC has commissioned the InterAcademy Council (IAC) to conduct an independent review of the processes and procedures of the IPCC in preparing its reports. The IAC review results will be discussed at this year's IPCC Plenary Session and reflected in the IPCC Fifth Assessment Report (to be released in 2013-2014).

In this column, we explain about questions you might have regarding global warming based on scientific knowledge offered in the IPCC AR4 and other documents.

(1) Is there sufficient evidence that anthropogenic

greenhouse gases are the major cause of global warming?

Not only anthropogenic factors such as greenhouse gas emissions but also natural factors including solar activity and aerosols discharged by volcanic eruptions cause changes in the global mean temperature, and a combination of various factors leads to temperature rises or decreases. Around the mid- $ 20^{th} $ century, there were periods when the global mean temperature stayed flat despite higher atmospheric concentrations of greenhouse gases due to other offsetting factors. The IPCC AR4 noted that based on the results of climatic simulations for 1906-2005, rapid global warming observed in the recent several decades cannot be reproduced without considering anthropogenic increases in greenhouse gas emissions.

(2) The biggest greenhouse effect comes from water vapor. So, isn’t it true that a small increase in carbon dioxide emissions has little impact on the environment?

It is true that water vapor has the biggest greenhouse effect (about 60%), but carbon dioxide also plays an important role by contributing about 30% of the greenhouse effect. The amount of water vapor in the atmosphere is determined by exchanges

to storm-surge flooding (Western Japan), and ¥119.2 billion in cost of damage due to heat stress (heat stroke) (evaporation and precipitation) between the atmosphere and oceans/land surface. Thus, the amount of water vapor does not increase or decrease significantly due to human activities. Water vapor is believed to grow in amount in the atmosphere if temperatures rise which increasingly accelerates global warming, but much more contributory to temperature rises are carbon dioxide emissions by human activities. In other words, due heed certainly needs to be given to water vapor in that water vapor currently is a factor for the greenhouse effect and has potential to amplify global warming in the future. In order to contain the progression of global warming, however, it is more effective to curb emissions of carbon dioxide and other greenhouse gases.

(3) Isn’t it true that the major cause of global warming is animated solar activity, etc. and not the increase in greenhouse gas concentrations?

As noted in (1), not only the increase in greenhouse gas concentrations but also animated solar activity (an increase in radiant energy from the sun) and other factors cause to alter the global mean temperature. However, the latest observation data on the number of sunspots, a good indicator of solar activity, shows that sunspots have stayed almost flat or tended to decrease since the mid- $ 20^{th} $ century, indicating little possibility of solar activity becoming more vigorous. Cosmic rays (electric atomic nuclei drifting in outer space) that reach the earth’s atmosphere are said to form clouds, and there is a theory that cosmic rays decrease when solar activity becomes vigorous and a resultant reduction in the amount of clouds causes temperatures to rise. At present, however, there is no established correlation between cosmic rays and the amount of clouds and the physical mechanism involved has not been elucidated. After assessing scientific discussions concerning natural factors such as solar activity and cosmic rays, the IPCC AR4 has concluded that the increase in global average temperatures in the latter half of the $ 20^{th} $ century is very likely due to the increase in anthropogenic greenhouse gas concentrations.

mortality, respectively, is estimated each year in the 2090s.

## Section 2 Economic Effects of Measures to Cope with Global Warming

Measures to cope with global warming are believed to have both positive and negative effects on the economy. As specific positive effects on the economy, considerable new business opportunities are conceivable in a diverse range of industries and services. The market for low-carbon energy products is one of fields with considerable potential going forward. Japan must strive to take advantage of these business opportunities.

Measures to deal with climate change may also help eliminate existing inefficiencies. At the corporate level,