In 2007, the Intergovernmental Panel on Climate Change (IPCC) published its 4th Assessment Report (AR4) after an unusual number of climate-related catastrophes, and after several consecutive years of record-high temperatures than ever before. was known up to now. The following conclusions were reached:
- The concentration of greenhouse gases in the Earth's atmosphere is directly related to the global average temperature of the planet.
- Since the Industrial Revolution, concentration has been increasing continuously and with it the global average temperatures.
- The most abundant greenhouse gas is carbon dioxide, which is generated by burning fossil fuels.
Greenhouse gases are naturally present and are essential for the survival of living beings, since among other things they prevent part of the Sun's heat from being reflected back into space, which makes life on earth possible. As populations and economies grow and living standards rise, so does the cumulative level of greenhouse gases.
AR4 evaluated the following evidence on the current world situation:
- The average temperature of the Earth's surface has risen 0.74ºC since the end of the 19th century.
- It is predicted that by the year 2100 it will have increased by an additional 1.8 to 4ºC if nothing is done to prevent it. This assumes a rapid and intense change in geological time.
- Even if it were "only" to rise by 1.8ºC that would be a greater temperature increase than in any other century in the last 10,000 years.
- Around 20-30% of plant and animal species are likely to be at increased risk of extinction if the global average temperature rises above the 1.5-2.5ºC range.
- The mean sea level rose between 10 and 20 cm throughout the 20th century. It is expected that by 2100 it will have risen between 18 and 59 cm more. Higher temperatures cause the volume of the oceans to expand. As glaciers melt, they add more water to the oceans.
- As the brilliant white of ice and snow gives way to dark navy blue, the ability to reflect the sun's rays is further reduced, intensifying warming.
It is not known for sure when the world's oil reserves will be depleted. Today coal, oil and natural gas drive the economies of the world, and almost all modern human activities generate carbon dioxide (CO2) that makes climate change extremely complex and linked to other complicated problems such as poverty, economic development and population growth.