More in previous columns Issues that must be addressed globally from a long-term perspective As, Three of the most important issues And so far in that problem "Insufficient energy resources, water and food", "Use and disposal of radioactive materials" I have compiled information about.

This time, the last of the three issues will be "rapid warming." With regard to global warming, various studies are currently being conducted all over the world, and there is not yet a scientifically established theory or analysis for that global warming.

Currently, for the time being, I trust the IPCC Fourth Assessment Report, Working Group I Report (hereinafter referred to as the IPCC Report), which was issued in 2007, as the most recognized view of global warming. I think there is no choice but to proceed with thinking. The figures and graphs below are all from that IPCC report. See the link below for the original text. https://www.env.go.jp/earth/ipcc/4th/syr_spm.pdf

Below is a summary of the parts of the IPCC report that are particularly related to CO2 and global warming, and finally my opinion.

● Is the earth really warming?

　When viewed on a scale of 150 years

　Temperature measurement method: Temperature measurement with a thermometer

• Increase of 0.74 ℃ in 100 years until 2005
• The speed of climb is accelerating.

When viewed on a 1300 scale

Temperature estimation method: Estimated using various natural materials such as tree rings, ice sheets, shells and foraminifera.

• Today is the warmest time in the last 1300 years.
• A sharp rise in temperature has been seen since the 20th century.

When viewed on a scale of 650,000 years

Temperature estimation method: Estimated from analysis of ice cores in Antarctica and Greenland

• The warm interglacial period and the cold interglacial period have been repeated about 5 times in the past 500,000 years, and it is now the interglacial period.
• In the previous interglacial period, there were times when the temperature was higher than the current temperature.

(summary)

1. ​There is no doubt that the earth has warmed in the last 100 years.
2. Moreover, the speed of the temperature rise is steadily increasing.
3. However, the current high temperature itself is within the range that can occur as a natural phenomenon.
4. The problem is not the high temperature, but the speed of warming too fast.

When viewed on a scale of 650,000 years

1. Last 650,000 years it was 180-300ppm.
   Immediately before the Industrial Revolution, it was about 280ppm.
   After that, it rose sharply and increased to 379ppm in 2005.
2. Moreover, the rate of increase in CO2 concentration is steadily increasing.
   The rate of increase in CO2 concentration during the 10 years from 1995 to 2005 is the highest since the observation from 1960.
3. The main reason for the increase in the concentration of CO2 in the Atmospheric air is due to human activity.
   Since 1750, it is estimated that about two-thirds of anthropogenic carbon dioxide emissions have come from burning fossil fuels and about one-third have come from changes in land use (such as deforestation and biomass corruption). ing.

● Is the increase in the concentration of greenhouse gases such as CO2 the main cause of global warming?

1. Most of the global mean temperature rises observed since the mid-20th century are quite likely caused by the increase in anthropogenic greenhouse gases.
2. The grounds for this include the following simulation results.
   If the effects of an artificial increase in greenhouse gases are taken into consideration as the conditions of the simulation, the data will be in good agreement with the actual temperature change data, but if they are not taken into consideration, the data will not be in agreement with the actual data.

(See the figure below)

● How much will global warming progress in the future?

The IPCC report describes the results of forecasting 100 years from 1980 to 1999 (2090 to 2099) in response to several greenhouse gas emission scenarios.

Temperature change 1.1-6.4 ° C increase over the next 100 years
Temperature changes over the past 100 years and forecasts of temperature changes by scenario over the next 100 years
(However, the orange line is not a forecast based on future scenarios, but a simulation result when the CO2 concentration as of 2000 is maintained)

● What kind of changes will occur due to global warming?

The IPCC report lists the following changes:

• Sea level rise 18 cm to 59 cm over the next 100 years However, if warming continues in thousands of years, it may rise by about 7 m with the disappearance of the Greenland ice sheet.
• Increased frequency of high temperatures and heat waves
• Increased frequency of heavy rain
• Increased areas affected by drought
• Increased activity of strong tropical cyclones
• Increased occurrence of extremely high tides
• Increased risk of water shortages, food shortages, heat waves, storms, floods, drought damage, infectious diseases, etc.
• Dozens of percent of species can face extinction risks with several degrees of temperature rise
• Increased water availability and agricultural yields in cold regions (high latitudes)

● My opinion

It seems almost certain that the increase in greenhouse gases such as CO2 caused by human activities is causing the rapid warming of the earth. However, simulation techniques such as the global climate and rising sea levels are still in the process of development and have never been established, and how serious will humankind suffer when warming further progresses? However, it seems that there are still many uncertainties. Even if CO2 from human activities accounts for a large part of the cause of global warming, even if the world cooperates to take measures from now on, it will be possible to stop the global warming for the next 100 years. As the forecasts based on future scenarios of global warming show, it will take 100 years or more, and in any case we will have to deal with the warming Earth for more than 100 years. It's certain.

So, of course, it is necessary to take measures to stop global warming, but it is certain that global warming will occur more than that, so it is better to focus on measures in case of global warming and minimize the damage. Shouldn't we focus on it? I think.

Furthermore, in terms of urgency, isn't it necessary to prioritize the problem of "shortage and soaring water, food and energy resources" over the reduction of CO2 due to global warming in the short term? I feel that.

Next time, I would like to summarize the currently possible countermeasures for the three major environmental problems mentioned so far.

December 15, 2008 Hironobu Matsui