Introduction: Over the past 150 years, global temperatures have risen dramatically, and people tend to go to the beach to escape the heat on increasingly hot summer days, but will the ocean really be the last piece of paradise?Recently, scientists have discovered that the ocean absorbs 90% of the heat generated by climate change, equivalent to the power of an atomic bomb per second** for the past 150 years. How are scientists studying global ocean warming, and what "superpower" technologies are being used?We invited Wei Ke, an associate researcher from the Institute of Atmospheric Physics, Chinese Academy of Sciences, to give us a talk!
There has been a lingering cloud in the understanding of climate change over the past 100 years, because all the observation sites for assessing climate change are mainly concentrated on the land surface of the continental region of the Northern Hemisphere, while the ocean surface and interior, which account for 71% of the earth's surface area, are not only sparse and short-sighted, which makes a large number of our studies and main cognitions of global change concentrated on the land surface and atmosphere, and also makes it very likely that the global temperature series will have a large deviation. Recent analysis of ocean data has gradually lifted this "dark cloud", revealing an astonishing fact: the global ocean is warming at an accelerated rate
If you ask aliens to name the earth, "water ball" or "blue ball" would be a good choice, in the universe the earth looks like a blue water ball, the ocean covers about 71% of the earth's surface area, the average thickness is 4 kilometers, and it stores 97% of the water resources. The total mass of the ocean reaches 14 10 18 tons, compared to which the total mass of the atmosphere is only 5 10 15 tons, which is only 036%。Furthermore, considering that the specific heat capacity of seawater is much larger than that of the atmosphere and land surface, the ocean has a stronger heat storage capacity and is the main regulator of global change.
Figure 1The oceans are a key component of the climate system. **From Neelin (2010) Climate Change and Climate Modeling
After being reflected by the atmosphere, clouds and surfaces, as well as absorbed by the atmosphere, only about 51% of the solar radiation entering the earth-atmosphere system can heat the earth's surface, and 70% of it is absorbed by the ocean, and then released in various forms of energy such as long-wave radiation and latent heat sensibility. Over the past 100 years, global greenhouse gases have gradually increased, causing the Earth system to "trap" more heat, directly driving global warming, more than 90% of this energy is stored in the oceans, so changes in ocean heat content are a central pointer of climate change: global warming is in fact ocean warming. When considering changes in global energy or heat, it is possible to get a more accurate picture of changes in the Earth's climate system, even ignoring changes in atmospheric and land surface temperatures, and only analyzing changes in ocean heat capacity.
There are tens of thousands of meteorological stations on the Earth's surface, the oldest of which has been making continuous observations for more than 200 years, which have played a crucial role in understanding the climate change on the land surface over the past 100 years, especially in the last 50 years. However, these observatories are mainly located in the continental regions of the Northern Hemisphere, and even in continental areas, they are also found to be Forests and glaciers are present, and the distribution of stations is not uniform, so the global temperature calculated based on the land surface only reflects one aspect of the entire climate system, and it is very likely that there will be a large deviation, which is a lingering shadow for the study of global climate change.
As global greenhouse gas concentrations continue to rise, global temperature increases have become an established fact, and the question of how much the ocean warms has not been effectively solved, mainly due to the lack of ocean observation data in the past, which is not only small in quantity, but also poor in quality. In addition to the need for long-term climate change monitoring, detailed marine data is also needed to deeply understand marine anomalies such as "El Niño", "La Niña", the Antarctic Circumpolar Current, the North Atlantic** and the Pacific Decadal**, and marine data is also an important basis for climate on seasonal to interannual time scales.
Since 1998, the international preparation for the establishment of ARGO (Array for Real-time Geostrophic Oceanography, abbreviated as ARGO, which is the name of the ship of the hero Jason in Greek mythology) global real-time ocean observation network, ARGO used automatic profile buoy is a cylindrical self-sinking floating device, about 15 meters and weighs about 45 kg (Figure 2). Once put into the sea, the buoy will automatically dive to a depth of 1,000 meters, drift with the current for several days (usually 10 days), dive another 1,000 meters, reach a depth of 2,000 meters, slowly rise, return to the surface of the ocean, and use its own electronic sensors to measure the temperature and salinity of the sea water layer by layer during the ascent process. When the buoy reaches the sea surface, it will automatically send the positioning and measurement data to the satellite, and then relay it to the data center, after which the buoy will dive again and enter the next observation cycle. This kind of buoy has the advantages of no routine maintenance, not susceptible to man-made damage, and can obtain a large area, deep ocean data for a long time, automatically, real-time and continuously"a revolution in the means of ocean observation". The buoys used by ARGO can operate automatically in the open ocean for 4 to 5 years until the battery capacity of the buoy is exhausted, and usually a buoy can obtain 140-180 profiles during its lifetime.
Figure 2Argo buoys.
Since the official implementation of the ARGO program in 2000, nearly 40 countries and groups around the world, including the United States, Australia, France, the United Kingdom, Germany, Japan, South Korea, India and China, have deployed more than 14,000 ARGO buoys in the global ocean, forming the global ARGO real-time ocean observation network, thus truly realizing the real-time observation of the global pelagic ocean. There are currently 3,925 ARGO buoys floating in the interior of the global ocean (January 6, 2019), providing continuous real-time monitoring of the state of the global ocean.
With the completion of the "Core ARGO" network and the continuous innovation and development of profile buoy technology, the plan proposes to continue to expand to the ice-covered polar sea area, the equator, the western boundary current area and the important marginal seas (including the Sea of Japan, the Mediterranean, the Black Sea, the Gulf of Mexico and the South China Sea), and derives two sub-projects, "Biogeochemical ARGO (BGC-ARGO)" and "Deep-sea ARGO". In the early days, ARGO buoys could not observe ice-covered sea areas, but today buoys equipped with ice-detecting sensors can surface to send observations after the buoy has drifted to ice-free sea areasIt is also possible to store the data temporarily and send it back to the surface after the ice sheet melts in the summer. Today, ARGO data has become an important source of data and reference in ocean and atmosphere research.
Argo data became truly abundant after 2005, when ocean observations were mainly ship-based, scarce, and mainly distributed in areas with abundant routes in the mid-latitudes of the Northern Hemisphere (Figure 3). How can we estimate the state of the ocean before the ocean observation data is insufficient?Scientists will never be able to travel back to the last century to re-make detailed measurements of the pelagic layer of the global ocean, so how to dig deep into the old data and regain the changes in the pelagic heat content of the ocean in the past 100 years, especially in the past 50 years, has become an important research topic for climate change research. Researchers in the field of marine data have been continuously improving the quality of old data and developing new technologies to more accurately reconstruct the state of the ocean in the past.
XBT is the most important temperature observation instrument for the subsurface layer from 1970 to 2001, accounting for 41% of all subsurface temperature data from 1970 to 2001. Although there are various problems with the observational data based on this instrument, such as very uneven distribution in time and space, and systematic bias in the data, this is the core part of the only historical data that is currently available.
Figure 5Marine disposable temperature measuring instruments include a probe, a launcher, a deck processing unit and a data display and recording instrument, in which the probe is the part consumed by launching into the water, which is generally a torpedo-shaped streamlined shape. A temperature sensor is mounted on the probe head, and the collected signal is transmitted to the ship's deck handling unit via a signal line. After the probe body enters the water, the electrode on the probe body forms a loop with the grounding wire through the seawater, and the temperature measurement circuit starts to work, and the depth of the probe body falls while collecting the seawater temperature, and after the probe body reaches the maximum depth, the copper thin wire is automatically disconnected to complete the measurement.
XBT data is often referred to as one of the "immature" data because of the systematic bias in XBT data. How do I correct XBT bias?How can I make better use of historical XBT data?From 2008 to the present, different international research groups have proposed more than 10 bias correction schemes to correct the systematic bias of historical XBT data. At the fourth XBT Scientific Symposium held in November 2014, the XBT research group made recommendations for the first time on how to use XBT data in the academic circles of climate change and physical oceanography, suggesting that the following factors should be taken into account when correcting XBT deviations: temperature and depth deviations need to be corrected at the same time, differences between different instruments need to be taken into account when correcting, the effects of different sea temperatures, and inconsistent deviations in different periods of history. In 2014, the research team of Zhu Jiang and Cheng Lijing from the Institute of Atmospheric Physics of the Chinese Academy of Sciences proposed a revised scheme for the deviation of marine data, which stood out and became the best revision scheme recommended in the world.
In addition, there are a large number of unmeasured areas in the ocean, and it is necessary to use existing observations to "extrapolate" the temperature changes in the unobserved areas. The physical basis of this "speculation" is that the movements of the various regions of the ocean are not independent, but are richly correlated. The research team of the Institute of Atmospheric Sciences has proposed a new spatial interpolation scheme using the rich spatiotemporal correlation of the ocean, which uses the ensemble optimal interpolation method and uses the multi-model historical simulation of the coupled model comparison plan to provide a dynamic ensemble sample to provide a better initial field (as a prior estimate) and background error covariance (which defines how information is transferred from the observed area to the non-observed area), which effectively overcomes the main problems of the current mainstream schemes. Based on the above development techniques, the research team reconstructed a new temperature dataset of the upper 2000 meters of the global ocean since 1940, and continuously updated the data, which is a grid of 1 degree and 1 degree horizontally, with a total of 41 layers from 1 m to 2000 m, and the monthly average temperature data from 1940 to the present.
Systematic analysis and evaluation show that the dataset can accurately reproduce the climate mean state, interdecadal variation (e.g., PDO), interannual variability (e.g., ENSO), and long-term trend in the historical interval from 1940 to 2015. In addition, the NCAR-led study compared the temperature data of the six most commonly used subsurface lattices (IPRC, Scripps, EN41. JAMSTEC77, IAP) estimates the energy budget of the Earth system between 2004 and 2014, and finds that the results based on subsurface temperature grid data have a large error on the intermonthly scale. Nonetheless, the grid data of the Institute of Atmospheric Sciences had the smallest error among the six observations used.
The new ocean warming estimates based on this set of data are about 13 per cent faster than those estimated in the Fifth Assessment Report of the Inter-Panel on Climate Change and reflect a faster rate of global warming. The study shows that climate warming is not slowing down from an energy perspective, but that the ocean and earth systems are absorbing heat at an accelerated pace, especially in the deep sea. In addition, more accurate estimates of ocean heat content solve the mystery of "disappearing energy" (i.e., the mismatch between the energy budget of the atmosphere top and changes in ocean heat content) that plagues the scientific community on climate change. The findings were published in the journal Science Advances in 2017 (Cheng et al.).Anderson et al., 2017), which was directly used by the Fourth National Climate Assessment of the United States-Climate Science Assessment Report, was selected by the Royal Society as one of the major developments after IPCC-AR5.
In addition, the smallest of the five estimates of changes in ocean heat content listed in the Fifth Assessment Report on Inter-Climate Change (IPCC-AR5) is only half of the largest estimate (Figure 6). On the one hand, the uncertainty in the estimation of ocean warming rate limits people's scientific understanding of global warming and affects the estimation of key climate parameters such as energy imbalance and climate sensitivity of the earth systemOn the other hand, it is also a great obstacle to the evaluation of climate models, which are impossible to evaluate the simulated state of climate models for past climate based on ocean data with large errors, and also limit the numerical models to make reasonable predictions of the future.
Figure 6Changes in ocean heat content in the upper 2000 m of the world: past changes and future projections. The spline on the right is the 2081-2100 estimate. The new ocean heat content estimates (blue) show a stronger rate of ocean warming over the same period than the five estimates in IPCC-AR5 (gray). Contemporaneous simulation results of climate models (yellow-green).
Recently, Cheng Lijing, associate researcher of the Institute of Atmospheric Sciences, Chinese Academy of Sciences, and J. Cheng of the University of St. Thomas in the United StatesAbraham, University of California, Berkeley, ZHausfather and the American Center for Atmospheric Research KTrenberth answers these questions in an article in Science (Cheng et al, 2019)。They re-estimated changes in the upper ocean heat content using the latest data on the upper 2,000 meters of ocean heat content from the Institute of Atmospheric Physics, as well as new data from the Japan Meteorological Agency, the Commonwealth Scientific and Industrial Research Organisation of Australia, Princeton University in the United States, and others, which have updated and improved their methods. The results show that the data show a very consistent upward trend in global ocean heat content since 1955 using the new methodology.
In the period 1971-2010, the rate of warming in the upper 2000 meters of the global ocean was 036~0.39 wm-2。New estimates show a stronger rate of ocean warming than IPCC-AR5: IPCC-AR5's estimate for the same period is only 020~0.32 wm-2。In addition, ocean warming accelerated significantly after the 90s: after 1991, the rate of warming over 2000 meters of the ocean was 055~0.68 wm-2。This is a direct reflection of the impact of greenhouse gases emitted by human activities on the ocean.
Can climate models accurately simulate past ocean changes?Science studies have shown that the Coupled Model Comparison Scheme 5 (CMIP5) model ensemble can on average simulate historical ocean warming very well: between 1970 and 2010, the rate of warming in the upper 2000 m of the ocean simulated by CMIP5 was 039 WM-2, which is almost consistent with the latest observations. The model's excellent simulation of the past greatly enhances its credibility in future projections. According to the CMIP5 model, it is estimated that in RCP8Under the 5 scenario (assuming no future climate policies to reduce emissions), the entire upper 2,000-metre ocean would warm by an average of 078 degrees Celsius (relative to the climate state of 1991-2005), which is 6 times the total warming of the oceans over the past 60 years!In RCP26 Under the scenario (assuming that future climate policies can approach or meet the goals of the Paris Agreement), the upper 2,000 meters of ocean warming would average by 04 degrees Celsius.
Human activities have profoundly changed the marine environment, and ocean warming has caused sea level rise, dissolved oxygen drop, exacerbation of extreme events, coral bleaching and other consequences. However, due to the "lag effect" of the ocean's response to greenhouse gases, the oceans are warming at an accelerated rate, and stronger ocean warming will occur this century. Even if the Paris Agreement targets are approached or met, ocean warming and its impacts will continue. If we don't respond proactively, we will face serious climate risks for both humans and the planet's ecosystems in the future.
Over the past 6-8 years, global warming stagnation (HIATUS) has become a hot topic in the field of climate change, and has given rise to a large number of science and nature levels**, as well as many more professions**. This concept is based on the fact that after the 1998 super El Niño, the global surface temperature increase was limited, for example, in the Fifth Assessment Report of the International Special Committee on Climate Change (IPCC-AR5), the global average surface temperature series showed that the average rate of increase since 1951 was 011±0.03 degrees Celsius for 10 years, while the average global surface temperature warming rate was only 005±0.10 degrees Celsius for 10 years, this is undoubtedly a manifestation of significant warming stagnation or slowing down. Some opponents of climate change skepticism have seized the opportunity to quickly stir up ideas such as the "warming lie" and the conspiracy theories that accompany it.
However, with the resurgence of temperatures after 2013, especially the 2015-2016 super El Niño, which caused the global temperature to soar, and the 1998 high temperature record quickly fell to 10 places, the concept of global warming stagnation suddenly seemed to be a "thing of the past". But how did the "stagnation" shown in the global surface air temperature data come about?Indeed, a more rational scientific explanation is needed.
If we look back at the climate change in the past 50 years using the data on global ocean heat content, we can find that there is no warming stagnation period in the ocean heat content series, and its change shows a steady growth trend. This suggests that if we want to examine the Earth's climate change, we need to consider the atmosphere and the ocean together, and that the ocean heat capacity is a more accurate reflection of what kind of climate change has occurred in the past few decades than the surface temperature series, given the huge area and huge heat capacity of the ocean. Because of global warming caused by the increase in global greenhouse gases, its heat distribution and flow are carried out throughout the climate system, and the recent "stagnation" of surface sea surface temperature changes is only a product of the natural variability of air-sea interactions, which is caused by the transport of ocean energy between different depths, and global warming has not stopped. When looking at the changes in the air-sea system, the term "global warming stagnation" (HIATUS) is basically a false proposition.