Will this year be the hottest?

The World Meteorological Organization (WMO) released an assessment report in May, predicting that there is a high probability that the high temperature record set in 2016 will be broken between 2023 and 2027.

Since the beginning of this year (as of June 30), the average number of days with high temperatures (maximum daily temperature ≥ 35°C) in my country is 4.1 days, 1.9 days more than the same period last year (2.2 days), the most in the same period since 1961.

**The northern land has experienced a scorching heat. **Compared with the same period in previous years, the eastern part of North China, the northern part of Northeast China, the western part of South China, the southern part of Southwest China, the southern part of Xinjiang, and the western part of Inner Mongolia have 5 to 10 days more than normal, and some areas have more than 10 days more. At the same time, the south has seen a significant drop in temperature, and many friends have said, "I want to go to the furnace city to escape the summer heat."

Is this year really hot? Will it be the hottest year ever? Let’s find out!

Image source network

1. What was the hottest year?

We first need to understand how "hottest" is defined.

This needs to be defined from two aspects: space and time. First, from a spatial perspective, **“hottest” means that the global average temperature breaks the record, not that the same high temperature occurs in all places at the same time. **Therefore, it is normal for the weather in the south of the Yangtze River to be cooler than that in the north in June, and the extreme high temperatures in Beijing, Tianjin and Hebei cannot mean that my country will usher in the hottest summer.

Secondly, from the perspective of time, the so-called "hottest" and "coldest" are not limited to the scale of one day or one month, but focus on the temperature throughout the year . Therefore, whether this year is the hottest year will not be known until the statistical results are released next year.

Last summer, heat waves swept across the country, with high temperatures of 40°C occurring frequently, and record-breaking temperatures becoming commonplace. In addition to my country, record-breaking extreme high temperatures also occurred in Central Asia, South Asia, Western Europe, and the United States. At the same time, throughout the year, high temperatures and severe cold events took turns, with North America and Europe suffering from severe cold and blizzards, and the sea temperature in the equatorial central and eastern Pacific Ocean being lower than usual. So, was last year the "hottest year" in the world?

Distribution of extreme maximum temperatures across the country from June 13 to July 12, 2022. A total of 71 national meteorological stations across the country recorded maximum temperatures exceeding historical extremes, including Lingshou (44.2°C), Gaocheng (44.1°C), Zhengding (44.0°C) in Hebei Province, and Yanjin (44.0°C) in Yunnan Province, with daily maximum temperatures exceeding 44°C. Source: National Climate Center

**2022 did not break the record of 2016 as the hottest year. **According to the "Global Climate Status Report (2022)" released by the China Meteorological Administration, the temperature in most parts of the world's land last year was close to normal to above normal, the fourth highest since 1850.

Let's talk about the "hottest year" since meteorological records began - 2016. Its average annual temperature was about 1.1°C higher than the pre-industrial level, directly approaching the goal of the Paris Agreement reached in the international climate change negotiations that year to limit global warming to 1.5°C.

According to data from the European Union's Earth Observation Program, Copernicus, the highest temperature ever recorded was 16.8°C, which occurred on August 13, 2016. The peak temperature this year occurred on June 9, which was only 0.1°C lower than the highest temperature record. Judging from the global daily average temperature, 2023 is likely to break the record for the warmest day in history.

Image source: Home | Copernicus

2. Why do the hottest years occur one after another?

Climate refers to the long-term average state of meteorological elements, which is usually relatively stable, such as the change of seasons in time and the huge difference in climate zones from polar to tropical regions in space. However, this stability also contains changes, so why does the climate change?

**The climate system is like a company,** consisting of five sectors: the atmosphere, ocean, land surface, cryosphere and biosphere. While each sector operates normally, it also exchanges matter and energy with other sectors, thus forming an open and complex system.

From the perspective of sources, the factors that can drive climate change can be divided into two categories:

**The first is natural factors,** which include external factors such as changes in solar radiation, collisions of extraterrestrial planets, and internal factors such as changes in the Earth's orbital parameters, volcanic activity, changes in land and sea, etc.;

**The second is human factors,** such as industrial emissions, deforestation, land reclamation, etc. In the past century, the role of human activities in climate change has become increasingly significant, and the view that human activities exacerbate the trend of global warming has been constantly emphasized. Despite this, the role of natural factors cannot be ignored, which will also drive the climate to produce periodic changes.

The five components of the climate system interact with each other. Image source: Internet

Since the formation of the modern atmosphere, the Earth's climate has switched back and forth between "icehouse" and "hothouse". Our Earth has experienced the snowy "snowball Earth" and has also become very warm in the Mesozoic Era. During the Quaternary Ice Age of more than 2.5 million years, humans quietly emerged and struggled with other animals for living space. The last ice age on Earth ended 10,000 years ago. The warm and humid climate conditions led to the emergence of primitive agriculture and the prosperity of human culture.

Since the Industrial Revolution, the traditional agricultural society has transformed into a modern industrial society. Intense human activities have had a profound impact on the planet, causing the current climate change to present an unprecedented warming trend.

Humans hunting mammoths during the Quaternary Ice Age (Source: Internet)

Modern society, industry, agriculture and urban development. Source: Internet

On March 20, 2023, the Intergovernmental Panel on Climate Change (IPCC) officially released the Sixth Assessment Report (AR6) Synthesis Report (SYR) "Climate Change 2023". The report pointed out that human activities have undoubtedly caused global warming, mainly by affecting the climate system through the emission of greenhouse gases. The global surface temperature from 2011 to 2020 has increased by 1.1℃ compared with 1850-1900. Human-induced climate change has caused frequent extreme weather and climate events around the world.

Image source: Global Zero Carbon

In meteorology**, when the temperature reaches or exceeds 35℃, it is called "high temperature weather", and high temperature weather for more than 3 consecutive days is called "high temperature heat wave event". **

In the absence of human activities, heat waves will occur once every 10 years on average. When the average temperature rises by 1.5°C, 2°C and 4°C, the frequency of heat waves will increase by 4.1 times, 5.6 times and 9.4 times, respectively, and their intensity will increase by 1.9°C, 2.6°C and 5.1°C, respectively.

3. Is this year's fever blessed by the "Holy Child"?

This year's heat wave is mainly due to the global warming and El Nino.

On May 17, the World Meteorological Organization released a report saying that global temperatures may reach record levels in the next five years due to the accumulation of greenhouse gases and the naturally occurring El Niño phenomenon.

On June 8, the National Oceanic and Atmospheric Administration (NOAA) issued an El Niño alert, which is expected to reach moderate to strong levels.

Recently, my country's National Climate Center predicted that the equatorial central and eastern Pacific will enter an El Niño state this summer, and the intensity may reach moderate or above.

my country's National Climate Center issued a reminder

El Nino, or "Holy Child" (Spanish for little boy, also for Holy Child) is here. El Nino and the La Nina that just ended are a pair of siblings. El Nino refers to the persistent and significantly warmer surface water temperature in the equatorial central and eastern Pacific, while La Nina refers to the persistent and significantly colder surface water temperature.

El Niño usually develops and grows in the northern hemisphere summer of the first year, reaches its peak in the winter, then gradually weakens and ends in the spring and summer of the second year, but it may also last for 2-3 years.

**The occurrence of El Nino often exacerbates the rise in global average temperature and creates the record for the warmest year. **The last super-strong El Nino phenomenon occurred from 2014 to 2016, creating the hottest year on record so far, 2016.

In the year of El Nino-La Nina, the global average temperature will change by about 0.1-0.2℃. **The occurrence of El Nino will increase the probability of extreme climate events and intensify global warming within 1-2 years. **That is to say, if El Nino develops and grows this year, the speed of global warming will accelerate, and it may refresh the highest average temperature since 1880.

Visualization of average temperatures over the years. The base map is from NASA, and annotations are provided by Chinese meteorological enthusiasts.

Image source: China Weather Network

But this year's heat is not entirely due to El Niño. In 2016, the peak temperatures were concentrated in the high latitudes of the northern continents, such as Siberia and the Arctic; in 2023, not only the northern continents were not spared, but even Antarctica experienced high temperatures. **Sea surface temperatures have been at record highs this year due to a series of marine heat waves around the world. **In February this year, the Antarctic sea ice area was only 1.79 million square kilometers, setting a record for the smallest sea ice area in history. On June 11, the temperature in the North Atlantic reached a peak of 22.7℃, 0.5℃ higher than the highest record in June 2010.

What is causing the ocean to heat up? Research suggests that weakening trade winds due to changes in atmospheric dynamics is the most likely cause. In the North Atlantic, weakened winds may have reduced the amount of dust blowing in from the Sahara Desert, which normally helps cool the ocean, and the reduced dust has therefore caused the ocean to heat up.

Time series of changes in heat content in the upper 2000 m of the global ocean from 1958 to 2021

Will the emergence of El Nino necessarily lead to the "hottest year"? According to statistics, since 1980, the global average temperature record has been broken ten times in El Nino years. But whether it can break the hottest record in 2016 depends on its intensity and duration. Meteorological experts analyzed that this year's ocean background is very different from last year. The increase in precipitation in the south can suppress high temperatures to a certain extent. This summer may not be as hot as last year, but this winter is likely to be a warm winter.

El Nino will have an impact on the global climate, and abnormal climate will occur in many places, but the manifestation and impact on different regions are also different. What impact will it have on China's climate? China may have to face two significant impacts:

One is this year’s warm winter;

The second is the extreme precipitation and flood disasters that may occur in the Yangtze River Basin next summer.

4. What are the hazards of high temperature?

On June 13, the European Environment Agency released data showing that since 1980, extreme weather in Europe has caused nearly 195,000 deaths and economic losses of more than 560 billion euros. Heat waves play an important role, accounting for 81% of deaths and 15% of economic losses.

The impact of global warming. Image source: WRI

**In terms of disaster risk, high temperatures accelerate water evaporation, causing rivers to dry up and reservoirs to dry up. **As the climate warms, the number of combined extreme events of high temperatures, droughts and wildfires increases. Wildfires not only cause serious local air pollution, vegetation destruction and loss of life and property, but also release a large amount of carbon dioxide, which may further aggravate global warming and form a vicious cycle.

**In terms of food security, July and August are the key periods for the formation of rice yield in my country. Continuous high temperatures will affect its fertilization and ear differentiation, increase the empty and barren rate, and cause a reduction in yield. **The reduction in the yield of major crops will undoubtedly have a great negative impact on life safety and social order.

**In terms of public health, high temperature heat waves have a significant impact on human health and mental health. **The impact of hot days on people is not simply to turn on the air conditioner more often and stay at home less. For people who are vulnerable to climate change, especially the elderly, patients with chronic underlying diseases, and outdoor workers, their health is directly threatened, the probability of suffering from heat stroke and heat stroke has increased sharply, the risk of cardiovascular disease has increased, and even life safety has been affected.

I hope everyone will pay close attention to the meteorological department's research and forecasts, and use scientific knowledge to protect life, property, and production safety. We will wait and see whether this year will become the "hottest year".

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Author: Associate Professor Li Beibei from the Institute of History of Science and Technology and Meteorological Civilization, School of Law and Politics, Nanjing University of Information Science and Technology

Gong XinyuMaster