Many places are so hot that people are "doubting life". Is it all caused by El Niño?

Do you also feel that this summer seems to be getting hotter earlier than usual? As early as May, many parts of the world saw high temperatures above 38°C, and some even exceeded 41°C. Since June, the temperature in many parts of northern my country has exceeded 40°C. Many people have expressed on social networking sites that it feels so hot that they are "doubting their lives."

Why is this summer so hot? Some say it is a manifestation of global warming, while others say it is related to El Nino. What is the truth? What does meteorology think of the "menacing" El Nino?

Copyrighted images from the gallery, unauthorized reproduction, please contact the original author

1. The recent heat wave sweeping across the Northern Hemisphere and the spreading wildfires in Canada, are they both related to El Niño?

Anyone who has studied geography in middle school knows that the Pacific subtropical high pressure is the main weather system that affects the distribution of rain and heat in my country in summer. In midsummer, areas controlled by the subtropical high pressure are often areas where high temperatures are concentrated. The west and north sides of the subtropical high pressure are usually where cold and warm air currents converge, and heavy rains often occur here.

This year is the year of development of El Niño. Under the interaction of the ocean and the atmosphere, the El Niño event may affect the distribution of rain and heat in my country by affecting the two major weather systems, the monsoon in East Asia and the subtropical high pressure in the western Pacific.

In May this year, South China should have been in the heaviest precipitation period of the year - the Dragon Boat Festival period. However, the subtropical high pressure in the western Pacific was abnormally strong and its position to the north had arrived in South China ahead of schedule. In addition, the downward airflow around this year's No. 2 typhoon "Mava" had a warming effect. The combination of the two caused South China to experience extremely high temperatures and heat waves that were rare in the same period in history. To some extent, this was also a response to the development of El Niño. When El Niño occurred, the intensity of the subtropical high pressure in the western Pacific was strengthened.

In June, a heat wave swept across the northern hemisphere and wildfires raged in Canada. These can be said to be related to El Nino, but the more important factor is not this. Against the backdrop of global warming, the frequency of extreme weather events is increasing, and the occurrence and development of El Nino may bring about an amplifying effect.

2. It came 1-2 months earlier than expected. Is this El Niño still developing?

According to current forecasts, this El Niño will come 1-2 months earlier than expected and develop faster than expected, and its impact on temperature may be apparent in 2023. Therefore, 2023 or 2024 will most likely set a new global warming record.

However, the prediction of El Nino is not a done deal. According to Ding Yihui, an academician of the Chinese Academy of Engineering and a meteorologist and climatologist, spring is the first hurdle for the development of El Nino, which is called the spring barrier in the forecast. Because the wind is the most unstable in spring, if the westerly wind cannot "overwhelm" the easterly wind, then El Nino may "die".

After passing the spring hurdle, El Nino still needs to pass the "test" of July and August. There have been cases in history where El Nino disappeared in July and August. This is because July is still five or six months away from the peak of El Nino, just like a child is prone to premature death. Academician Ding Yihui pointed out that scientists are now very cautious about whether an El Nino event will occur, and they have to wait and see the sea temperature in July before they can make a conclusion.

So what is the current state of ocean temperature? According to the global ocean monitoring released by the National Climate Center, in April 2023, the sea surface temperature (SST) in most of the equatorial central and eastern Pacific was higher than the same period of previous years (Figure 1). The Niño3.4 area sea temperature index was 0.2℃, up 0.2℃ from the previous month (Figure 2), and the sliding average of the index in the last three months (February to April) was -0.1℃. The SST in most of the North Pacific and most of the mid-latitude waters of the South Pacific was significantly higher than the same period of previous years, among which the anomaly of the warm center in the North Pacific was above 1.5℃.

Figure 1. Distribution of sea surface temperature anomalies in April 2023 (℃) (Source: National Climate Center)

Figure 2 Monthly evolution of the sea surface temperature index (℃) and SOI index in the Niño 3.4 region (source: National Climate Center)

According to the El Nino and Southern Oscillation forecast released by the World Meteorological Organization in April, the probability of El Nino occurring from May to July this year is 60%. The National Climate Center predicts that the equatorial central and eastern Pacific will enter an El Nino state this summer.

Regarding the future development trend of El Nino, Michelle Leh, a climate expert at the National Oceanic and Atmospheric Administration of the United States, said that this El Nino phenomenon appeared early and has a large development space. The probability of developing into a strong El Nino in winter is 56%. If a strong El Nino occurs, 2024 will most likely become the hottest year on record. Globally, Indonesia and Australia will experience more droughts and fires, while eastern South America will experience more flood damage and extreme rainfall.

There are still uncertainties as to whether next year will be the hottest year in recorded history due to the influence of El Nino. The current forecast for this El Nino event is that it will be a moderate or above intensity event, and the meteorological department will closely monitor its development dynamics and changes in intensity.

3. Occurring an average of 3.5 times every decade, is El Niño becoming more frequent?

El Niño is a periodic natural phenomenon with an average life span of 11 months, ranging from 6 to 7 months to as long as 18 months. It occurs approximately every 2-7 years.

According to the national standard "El Niño/La Niña Event Discrimination Method" (GB/T33666-2017), a total of 21 El Niño events have occurred since 1950, including 11 weak El Niño events and 10 moderate and above El Niño events. In the 51 years from 1950 to 2000, there were 14 El Niño events, an average of about 2.7 times per decade. In the 20 years since the 21st century (starting in 2001 and ending in December 2020), a total of 7 El Niño events have been monitored, an average of 3.5 times per decade. It can be seen that the number of El Niño events has increased since the 21st century.

Figure 3 El Niño intensity classification. El Niño is divided into five levels: weak, weak, moderate, strong and extremely strong El Niño.

If we only consider strong El Nino events (with a peak intensity above 2.0℃, which includes strong and super strong El Nino events in the national standard), there were 2 in the 50 years before the 21st century, and 1 after the 21st century. In terms of the distribution of central and eastern types of El Nino, there were 8 central El Nino events and 13 eastern El Nino events. Before the 20th century, the eastern El Nino events were the majority, while after 2001, the central El Nino events were the majority.

What are the Eastern and Central types? Let’s start from the beginning and see how the meteorological community monitors El Nino.

Figure 4 Frequency of different types of El Niño events from 1950 to 2020

4. Eastern type VS Central type: How do meteorologists monitor and identify El Niño?

Since 2000, it has been found that the sea temperature distribution of many El Niño events is different from that of typical El Niño events in the equatorial eastern Pacific. Moreover, the sea temperature anomalies are different in different regions, and the impacts are also very different.

In the early days, people divided the El Niño events according to the location where the temperature rise first appeared during the El Niño event, and some people divided them according to the time when the El Niño event occurred. But later people found that defining an El Niño event in this way was not rigorous enough. Therefore, people began to use the distribution of sea temperature anomalies when the El Niño event reached its peak to divide it. Of course, this is not a final conclusion, and the exploration of a more objective division method is still "in progress" in the scientific community.

In 2017, the China Meteorological Administration formulated and issued the national standard "Method for Distinguishing El Niño/La Niña Events", which is consistent with the monitoring indicators of most countries in the world, but the specific data processing methods are different.

In this standard, distinguishing between the eastern type and the central type becomes the focus - using the Eastern Type Index (IEP) and the Central Type Index (ICP) to determine the type of event.

During an El Niño event, if the absolute value of IEP reaches or exceeds 0.5℃ and lasts for at least 3 months, it is determined to be an eastern type event. During the event, if the absolute value of ICP reaches or exceeds 0.5℃ and lasts for at least 3 months, it is determined to be a central type event. If an event contains both of the above situations and there is a transition between the two types, the type where the event peak is located is defined as the event main type, and the other is the non-main type. The type of the entire event is based on the event main type.

This consideration takes into account the distinction between the eastern type and the central type events. The reason for such a careful distinction between the two types is that their impacts on my country are completely different. With a scientific classification, scientists can conduct comparative studies on the characteristics of different types of El Niño.

For example, the impact of a central El Nino on the climate of South America, the west coast of North America, and even Japan and New Zealand may be completely opposite to that of an eastern El Nino. A central El Nino will often cause the western United States to experience a "seesaw" climate distribution with dry weather in the north and wet weather in the south in winter, while when an eastern El Nino occurs, most of the western United States will experience a relatively wet climate in winter.

In my country, when the Eastern El Nino occurs, there are significant precipitation anomalies in the eastern part of my country from the autumn of the current year to the summer of the following year, and the area of ​​precipitation anomalies varies in different seasons. However, when the Central El Nino occurs, the relationship between most parts of my country and El Nino is not significant and the seasonal differences are large. In addition, the Eastern El Nino causes less rainfall in the eastern part of North China and Northwest my country and more rainfall in the Yangtze River Basin, while the Central El Nino causes more rainfall in the eastern part of North China and Northwest China and less rainfall in the Yangtze River Basin.

Looking back at history, no two El Niño events are exactly the same. The impact on my country also depends on the seasonal process of the year and the comprehensive configuration of multiple systems. The specific situation needs to be analyzed specifically. When extreme weather becomes more and more frequent and even becomes a "new normal", how to effectively respond and reduce the risk requires everyone's deep thinking and action.

References:

1. Exclusive interview | What is the expected intensity and impact of this round of "El Niño"? The chief expert of the China Meteorological Administration explains in detail. The Paper. 2023.6.14

2. World Meteorological Organization: El Nino may return in the coming months. CCTV News Client. 2023.3.2

3. El Nino. China Weather Network. 2020.11.5

4. Experts interpret the El Nino climate phenomenon, which may bring a new peak in global warming. Guangming Daily. 2023.6.14

5. [Analysis] Take a calm look at the ongoing El Nino "heat". China Meteorological News. 2014.8.26

6. Popular Science Reading: The Fierce El Nino. China Meteorological News. 2015.8.1

7. Understanding El Nino from a single picture. China Meteorological News Agency. July 8, 2014

8. Six questions about El Nino. China Meteorological News. June 20, 2014

9. Things related to El Nino. China Meteorological News. 2020.5.22

Author : Li Qian, Lu Ting, Meteorological Film and Television Center of China Meteorological Administration

Reviewer : Xin Xin, Deputy Chief of Service, Meteorological Film and Television Center, China Meteorological Administration

Produced by : Science Popularization China

Produced by : China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.