Pearl Harbor: Bombed battleships' boost for climate science

Weather data from several ships bombed by Japanese pilots at Pearl Harbor has been recovered in a rescue mission that will help scientists understand how the global climate is changing.

Crew members aboard various vessels -- such as the USS Pennsylvania and the USS Tennessee -- died when their battleships were targeted in December 1941. Despite these losses, many boats returned to service during the Second World War and US naval servicemen continued their daily duties, which included recording weather data.

A new research paper, published in Geoscience Data Journal, tells the story of the recovery of World War II weather data that comes from 19 US Navy ships. Its rescue was made possible thanks to the hard work of over 4,000 volunteers who transcribed more than 28,000 logbook images from the US Navy fleet stationed at Hawai'i from 1941-1945. Previous studies have suggested these years were abnormally warm. The new dataset, encompassing over 630,000 records with more than 3 million individual observations, will help to show whether this was the case.

Dr Praveen Teleti, the University of Reading research scientist who led the research, said: "Disruptions to trade routes in World War II led to a significant reduction in marine weather observations. Until recently, records from that time were still only available in classified paper documents. The scanning and rescuing of this data provides a window into the past, allowing us to understand how the world's climate was behaving during a time of tremendous upheaval.

"There are two sets of people we need to thank for making this mission a success. We are very grateful to the global team of citizen scientists for transcribing these observations and creating a huge dataset that includes millions of entries about air and sea surface temperatures, atmospheric pressure, wind speed, and wind direction.

"The greatest respect must go to the brave servicemen who recorded this data. War was all around them, but they still did their jobs with such professionalism. It is thanks to their dedication and determination that we have these observations 80 years on."

Data from devastated ships

The logbooks used in the project come from 19 different ships, including battleships, aircraft carriers, destroyers, and cruisers, most of which played pivotal roles in World War II events. Many ships that data was recovered from were present at Pearl Harbor during the attack by Japanese bombers on 7 December 1941, although all ships listed in the study saw action in the Pacific at some point during the war. USS Pennsylvania was hit when Pearl Harbour was attacked by the Japanese air force in December 1941. One bomb fell on the battleship and caused the deaths of nine servicemen, but it remained in service. The USS Tennessee was bombed twice in December 1941, resulting in the death of five servicemen. It returned to service in February 1942.

Future climate studies

Observations from naval vessels were the primary sources of marine observations for the World War II period but many records were destroyed as an act of war, or simply forgotten due to the length of time they were considered classified.

The recovered dataset reveals how wartime necessitated changes in observation practices. For example, more observations were taken during daytime than nighttime to reduce exposure to the enemy ships and avoid being detected. It is believed that changes such as this could have led to slightly warmer temperatures being recorded, meaning today's history books show a period of abnormal warmth in global datasets during World War II. The new data will help resolve this uncertainty.

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Researchers correlate Arctic warming to extreme winter weather in midlatitude and its future

A warmer Arctic has been linked to extreme winter weather in the midlatitude regions. But, it is not clear how global warming affects this link. In a new study, researchers from Korea and USA show, using weather data and climate models, that while the "Warm Arctic-Cold Continent" pattern will continue as the climate continues to warm, Arctic warming will become a less reliable predictor of extreme winter weather in the future.

Pictures of melting glaciers and stranded polar bears on shrinking sea ice in the Arctic are perhaps the most striking images that have been used to highlights the effects of global warming. However, they do not convey the full extent of the consequences of warmer Arctic. In recent years, there has been growing recognition of the Arctic's role in driving extreme weather events in other parts of the world. While the Arctic has been warming at a rate twice as fast as the global average, winters in the midlatitude regions have experienced colder and more severe weather events. For instance, the winter of 2022-2023 saw record-breaking cold temperatures and snowfall in Japan, China, and Korea. Similarly, many parts of Eurasia and North America have experienced severe cold snaps, with heavy snowfall and prolonged periods of sub-zero temperatures.

While there are multiple theories for this climate phenomenon, an international team of researchers led by Professor Jin-Ho Yoon from Gwangju Institute of Science and Technology (GIST), Korea set out to examine the relationship between the severe winters in the Northern Hemisphere and the melting sea ice in the Arctic region, a phenomenon referred to as the "Warm Arctic-Cold Continent" (WACC), and how this relationship changed with the warming climate.

In their study published online on 27 March 2023 in the journal npj Climate and Atmospheric Science, the researchers looked at historic climate data and turned to climate projection models to explore the potential connection and assess how this phenomenon might be influenced by different global warming scenarios.

Based on the climate data from the European Center for Medium-Range Weather Forecasting (ECMWF) going back almost 40 years, the researchers correlated winter temperatures in East Asia and North America to the temperatures of the Barents-Kara Sea and the East Siberian-Chukchi Sea in the Arctic region. They observed that lower winter temperatures in East Asia and North America are usually accompanied by warmer Arctic Sea temperatures. However, they also found that in some winters, such as the 2017/18 winter in East Asia, this pattern did not hold, suggesting that this linkage include uncertainty likely due to factors other than Arctic Sea temperatures were at play.

Nonetheless, using climate projections from the Half degree Additional warming, Prognosis and Projected Impacts (HAPPI) experiments which were targeted to project future climate under 1.5°C to 2°C warming scenarios, the researchers found the WACC pattern to persist even when global temperatures rose. However, they found that the correlation between the Arctic Sea temperature and the East Asia temperatures became more uncertain with the intensification of global warming. "We found that the relationship between Arctic warming and cold weather events in midlatitude would become more uncertain under warmer climates, challenging the forecast of winter temperature in the future," says Mr. Yungi Hong, a Ph.D. student at GIST and a member of the research team.

"Our study shows that while one can expect the Arctic warming-triggered cold waves in the midlatitudes to persist in a warmer future, they will become more difficult to predict," adds Prof. Jin-Ho Yoon.

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