Climate change refers to long-term changes in temperature and weather patterns that may be natural but since the middle of the 18th century, the trends have changed. 

Human activities mainly due to burning fossil fuels (such as coal, oil, and gas) have increased the gases. 

The gases trap and the heating process develops, which is named as “greenhouse effect”. Such an effect is the cause of climate change which has had extensive effects on the environment.

The ice sheets in polar areas and natural lakes are shrinking, the rivers and lakes are disintegrating faster, the geographical ranges of plants and animals are changing and the trees bloom earlier. 

Scientists have predicted the consequences for the long term, that would come later due to global climate change, which is happening now, such as the loss of lakes, increasing the water level in the oceans, and longer and more intense heat waves. 

Generally, a wide range of published evidence shows that the net cost of damages caused by climate change is significant and will increase over time.

The sea level has increased from 1.7 mm per year in most years of the 20th century to 3.2 mm per year since 1993. The average thickness of the 30 well-studied natural lakes has decreased by more than 18 meters since 1980.

The area covered by sea ice in the Arctic at the end of summer has shrunk by about 40% since 1979. The amount of carbon dioxide in the atmosphere increased by about 25% from 1958 to 2020 and by about 40% after the industrial revolution.

The snow melts earlier than the long-term average. Flooding is now an increasing risk because our climate is changing. In comparison with the beginning of the 20th century, heavy and frequent rainstorms occur abnormally in regions like Iran, especially at unexpected times and frequency (like March 2019 and July 2022). 

The drought is getting worse. Humans use more water, especially for agriculture. Just like when the weather is hot, we sweat more, and higher air temperature causes us to lose more water, which means that the farmers should consume more water. 

Both highlight the need for more water in places where water reserves are decreasing.

Snow is an important source of fresh water for many people. As the snow melts, fresh water becomes available for use, especially in areas like Iran where there is not much rainfall during the warmer months. 

But as it gets warmer, it generally snows less and snow begins to melt earlier in the year, meaning snow may not be anymore a reliable source of water supplies.

Some changes (such as droughts, fires, and heavy rainfall) are occurring faster than scientists had previously estimated. UN Panel on Climate change (IPCC) - The United Nations body that was established for the scientific assessment of climate change on an inter-governmental scale- has determined that modern humans have never seen the changes observed in our world's climate before, and some of these changes will be nonrefundable for thousands of years.

Global warming

Scientists are very confident that the Earth's temperature will continue to rise for several decades, mainly due to greenhouse gases produced by human activity. 

The sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC) which was published in 2021, showed that the emission of greenhouse gases in the atmosphere before the industrial revolution (since 1750) has increased by 1.1 degrees Celsius. 

It is expected that the average global temperature in the next few decades will reach 2 (in some estimates 3) degrees of Celsius. This change will affect all regions of the Earth.  

The concept of average temperature for the entire globe may seem strange. However, at this moment, the highest and lowest temperature on earth is probably more than 55 degrees Celsius. 

They are far apart. Temperatures are getting worse from night to day. The times are different during the seasons in the northern and southern hemispheres. This means that some parts of the Earth are quite cold while other parts are quite hot. 

However, the concept of global average temperature measurement over time to identify and track changes in budgeting Earth's energy - how much sunlight is absorbed by the earth minus the amount that radiates into space as heat - is a useful concept.

Analyzing the surface temperature data of the similar ascending trend. The Earth’s surface temperature in each year from 1900 to 2020 in comparison with the average of 1981-2020 has an increasing trend. 

According to the May 2021 climate report, every month of 2021 was warmer than the average. The coldest month was February, which was 0.65 degrees Celsius warmer than the average. 

The temperature for the rest of the year was higher more than 0.8 degrees Celsius.

The Year 2021 with a temperature of 0.84 degrees Celsius higher than the average of the 20th century, was the sixth hottest consecutive year recorded on the planet. 

The years 2013-2021 are all among the ten warmest years on record. The year 2021 was also the 45th consecutive year (since 1977) with global temperature, at least nominally, higher than the average of the 20th century. 

Since 1880, the average temperature of the Earth's atmosphere rise has been 0.08 degrees Celsius. The average increase since 1981 has been 0.18 degrees Celsius, more than twice this rate.

The rate of global warming is not equal to the amount of carbon dioxide and other greenhouse gases that will be released in the coming decades. It depends on the emission in the atmosphere. 

Today, our activities - burning fossil fuels and destroying forests — release about 11 billion metric tons of carbon (equivalent to just over 40 billion square meters) each year. It adds carbon dioxide to the atmosphere (one metric ton of carbon dioxide fills a sphere with a diameter of about 10 meters). 

Since carbon is too much to remove in natural processes, atmospheric carbon dioxide is increasing every year.

What is the difference between climate change and global warming?

The severity of the effects of climate change depends on the direction of future human activities. The release of more greenhouse gases will lead to extreme weather events and widespread destructive effects throughout the planet. 

However, these future effects depend on the total amount of carbon dioxide we emit. Therefore, if we can reduce the emission of greenhouse gases, we may prevent some of the worst effects.

We think about climate change caused by human activity as something that will happen in the future, but this issue is a continuous process. 

Today, ecosystems and societies around the world are affected by climate change.

Climate change refers to something more than an increase in temperature and including sea level rise, changes in patterns, intensity, and recurrence of drought, water, energy, transportation, wildlife, agriculture, ecosystems, and human health.

The effects of climate change on different parts of society are related. Drought can harm food production and human health. The effects of climate change are felt in all aspects of the world in which we live. 

However, the effects of climate change are uneven across countries and the world— even within a single community, the effects of climate change can vary between neighborhoods or individuals. 

Long-term socio-economic inequalities can make disadvantaged groups, who often have the most exposure to risks and the least resources to respond, more vulnerable.

Iran and climate change

In the coming decades, Iran will face an increase of at least 2.6 degrees Celsius in the average temperature and a 35% decrease in rainfall. 

Iran is the first country responsible for climate change in West Asia and the seventh country in the world by emitting a total of 616,741 million tons of CO2. 

Iran's high-level share in greenhouse gas emissions is due to significant production and consumption of oil, and gas and rapid urbanization. 

Abnormality reduction in rainfall data and increase in rainfall data, upward radiation of long waves makes the effects of global warming and climate change intensify. 

Iran submitted the 1st and 2nd national reports in 2003 and 2011, respectively, to the United Nations Framework Convention on Climate Change (UNFCCC). 

In 2017, the third national report is submitted to the UNFCCC. Uncoordinated inter-departmental collaboration, insufficient collection of data and information as well as international sanctions prevent the implementation of Iran in the Climate change adaptation program.

The future and climate change

Forecasting the future under the effect of climate change is inevitable. Many of the problems and solutions are now known to us, and ongoing research continues to provide new ones. 

Experts believe that there is still time to prevent the most negative consequences by limiting the heat. 

Reducing the emission of greenhouse gases as soon as possible requires investment in technology and new constructions that cause employment growth with environmental considerations. 

In addition, such progress would reduce greenhouse gas emissions, reduce the harmful effects on human health, and save countless lives and billions of dollars in associated costs.

Changes in weather patterns can endanger life. Heat is one of the deadliest atmospheric phenomena. As the temperature of the atmosphere increases, storms become stronger and more humid, which can cause direct deaths and injuries.

Dry conditions lead to more forest fires, which pose greater health risks. The Indian Ocean monsoon phenomenon, which was mainly limited to the coastal areas, now affects areas as far as northern India (Himalayas) and northern Iran (Alborz) and has caused loss of life, damage to food sources, and as a result, threatens the health of more people.

Climates are more at risk. But public health groups can work with local communities to help people understand and build resilience to the effects of change.

Climate change and the past

Mass extinctions are the main drivers of macroevolutionary change. They are in geological history and show the basic transitions in the history of the Earth. 

The previous five major extinctions occurred around 450 million years ago (end of Ordovician), 350 million years ago (end of Devonian), 250 million years ago (end of Permian), 200 million years ago (end of Triassic), and 66 million years ago (end of Cretaceous and beginning of Paleogene) have occurred. 

However, the effect of environmental disturbance and biological response, which occurs on time scales below a thousand years, is still to be understood. 

End of the Permian mass extinction about 250 million years ago, there was a severe loss of marine and terrestrial organisms in such a way that about 80 % of the species disappeared. 

These extinctions in the past 542 million years - from the beginning of the formation of the first living organisms at the end of the Precambrian and the beginning of the Cambrian - have been identified.

Proposed drivers of mass extinctions are known as the Meteorites collision, volcanoes, floods, the world's lack of oxygen, and the high level of carbon dioxide in the atmosphere to the high temperature of the world as a mechanism for the killing of organisms and extinction. 

Although the geological records are full of all these occurrences, very few lead to mass extinctions. Studying the details of the time of past mass extinctions make it possible to determine the future trend of present-time climatic changes and possible subsequent extinctions (the sixth extinction).

The author is the head of the geology division, the Academy of Sciences, Tehran, Iran