The ocean covers more than 70% of the earth's surface and is the main driving force of weather and climate. A slight fluctuation of ocean temperature may lead to drastic changes in weather and climate around the world. The theme of this year's World Meteorological Day is "Oceans, Our Climate and Weather". Next, we will unveil the mystery of the ocean through a set of big data to see how the ocean is developing and how it affects our weather and climate.
From the perspective of space, the earth is more like a blue "water ball". (Image source: National Satellite Meteorological Center)
What kind of "butterfly effect" will happen when the ocean temperature changes by 0.5 ℃?
"A butterfly in the Amazon rainforest in South America can cause a tornado in Texas two weeks later by occasionally flapping its wings." This is the famous "butterfly effect". As the main driver of weather and climate, the subtle fluctuations of the ocean will undoubtedly lead to climate anomalies in many parts of the world.
Taking temperature as an example, an El Ni ñ o event generally occurs when the sea surface temperature in the equatorial central and eastern Pacific Ocean is higher than 0.5 ℃ and lasts for more than 6 months. When the El Nino event occurs, the number of tropical cyclones on the ocean is relatively small but the intensity is relatively strong. Severe drought may occur in northern South America, Australia, and Southeast Asia, while more rainfall may occur in central and southern South America, which is likely to cause floods. However, warm winters often occur in China, and rainfall generally presents a pattern of "waterlogging in the south and drought in the north".
When the sea surface temperature in the equatorial central and eastern Pacific Ocean is lower than 0.5 ℃ for more than 6 months, a La Nina event will occur. When the La Nina event occurred, the number of tropical cyclones on the ocean was generally on the high side. Drought often occurred in central Africa, southeastern United States and other places, while floods were prone to occur in northeastern Brazil, India and southern Africa. However, cold winter often occurs in China, and the rainfall pattern is dominated by "drought in the south and waterlogging in the north".
However, the factors affecting weather and climate are very complex and uncertain. Although El Ni ñ o and La Ni ñ a are one of the main factors affecting global climate change, we cannot simply say that any climate anomaly is the impact of El Ni ñ o or La Ni ñ a.
Note: See the end of the text for the detailed determination criteria of El Nino and La Nina.
The ocean is warming. The warming rate of China's offshore is higher than the global average
According to China's Population, Resources and Environment, Ocean Change and Its Role in China's Climate published in 2020, in the context of climate warming, since the middle of the 20th century, the global land and ocean surface warming has been very obvious. During the 61 years from 1958 to 2018, the global average sea surface temperature increased by about 0.54 ℃, and the average sea surface temperature in China's offshore areas increased more than the global average.
Global sea level accelerated to a new high
The warming and expansion of seawater, coupled with the melting of terrestrial glaciers and polar ice sheets, together led to the accelerated rise of the global average sea level. The monitoring shows that from 1993 to 2019, the global average sea-level rise rate was about 3.24 mm per year, reaching the highest since satellite observation records were available in 2019.
The sea level changes along China's coast also show an upward trend. The 2019 China Sea Level Bulletin shows that from 1980 to 2019, China's coastal sea level rose at a rate of 3.4 mm/year. From the 10-year average, the average sea level in 2010-2019 was at the highest level in nearly 40 years, about 100 mm higher than that in 1980-1989. It is estimated that in the next 30 years, China's coastal sea level will rise by 51-179 mm.
The proportion of strong tropical cyclones in the world is increasing and the intensity is increasing
Under the dual influence of ocean warming and climate warming, since 1970, the intensity of global strong tropical cyclones (strong hurricanes and typhoons) has increased and become frequent, causing major disasters in many regions of the world. Among them, the proportion of strong tropical cyclones formed in the west of 140 ° E in the northwest Pacific Ocean increased by 16% - 20%, and the frequency almost doubled.
The annual average maximum intensity of tropical cyclones in the northwest Pacific also shows an increasing trend, especially after 1980. At the same time, the position where the tropical cyclone reached its maximum intensity also moved northward, which also led to an increase in the average intensity of tropical cyclones landing in Japan, the Korean Peninsula and eastern China.
There are many types of marine disasters, which are most affected by storm surge in China
Marine disasters refer to disasters that occur at sea or on the coast due to abnormal or drastic changes in the marine natural environment. The most common types of marine disasters are storm surges, waves, sea ice, tsunamis, red tides, green tides, etc. From a worldwide perspective, storm surge disasters rank first in marine disasters. China, the United States, the Netherlands, and the Bay of Bengal have all experienced severe storm surge disasters. Japan is the country that suffered the most from earthquake and tsunami in the world. On March 11, 2011, the huge tsunami triggered by the earthquake caused devastating damage to Iwate, Miyagi, Fukushima and other places in northeastern Japan, and triggered the nuclear leakage of Fukushima Daiichi Nuclear Power Station.
China is a big maritime country, bordering the Pacific Ocean in the east, with a coastline of more than 18000 kilometers long. In the context of global warming, coastal marine disasters occur frequently and have a wide range of impacts. The main marine disasters in China are storm surges, waves and sea ice disasters. Red tide, green tide, seawater intrusion, soil salinization, saltwater intrusion and other disasters also occur to varying degrees.
Storm surge is the most important marine disaster in China. According to the statistics of China Marine Disaster Bulletin, the vast majority of direct economic losses caused by all marine disasters in China in the past decade are caused by storm surges. In 2014, 2015 and 2019, the direct economic losses caused by storm surge even accounted for 99% of the total losses.
Ocean, climate and weather are inextricably linked, which can be said to affect the whole body. With the rapid development of marine economy, the risk of marine disasters in coastal areas has become increasingly prominent, and the situation of marine disaster prevention and reduction is also very serious. Therefore, it is more important than ever to strengthen ocean observation and research, strengthen the ability of forecasting and early warning, and improve the public's awareness of risk prevention. (Planning/Zhang Fangli Design/Ren Chengying Data Support/Wang Weiyue and Hu Xiao)
Definition: El Nino and La Nina
El Nino event refers to the phenomenon that the sea surface of the equatorial central and eastern Pacific Ocean continues to be abnormally warm in a large range. At present, the National Climate Center of the China Meteorological Administration mainly uses the SST anomaly index of the NINO comprehensive area (NINO 1+2+3+4 area) as the basis for determining an El Ni ñ o event. The indicators are as follows: the SST anomaly index of the NINO comprehensive area lasts for more than 6 months ≥ 0.5 ℃ (there can be a single month in the process that fails to meet the indicators) as an El Ni ñ o event; If the index of this area lasts for 5 months ≥ 0.5 ℃, and the sum of the indexes of 5 months ≥ 4.0 ℃, it is also defined as an El Ni ñ o event.
La Nina event refers to the phenomenon that the sea surface temperature in the equatorial central and eastern Pacific continues to be abnormally cold in a large range. At present, the National Climate Center of the China Meteorological Administration mainly uses the SST anomaly index of the NINO Z region as the basis for determining the La Nina event. The indicators are as follows: the sea surface temperature anomaly index of NINO Z zone lasts for at least 6 months ≤ - 0.5 ℃ (during the process, there may be a single month that fails to reach the indicators), which is a La Nina event; If the index of this area lasts for 5 months ≤ - 0.5 ℃, and the sum of the indexes of 5 months ≤ - 4.0 ℃, it is also defined as a La Nina event.
