A new reconstruction of global average surface temperature change over the past 2000 years has identified the main causes for decadal-scale climate changes. The result shows that the Earth's current warming rate, caused by human greenhouse gas emissions, is higher than any warming rate observed previously. The researchers also found that airborne particles from volcanic eruptions were primarily responsible for several brief episodes of global cooling before the Industrial Revolution of the mid-19th century.
This new temperature reconstruction also largely agrees with other climate model simulations for the same period of time. The researchers found agreement for changes in temperature caused by identifiable factors, such as volcanic aerosols and greenhouse gases, as well as random fluctuations in climate that took place on the same timescales. This suggests that current climate models accurately represent the contributions of various factors that influence global climate change and are capable of correctly predicting future climate warming.
The research team working on the Past Global Changes (PAGES) project used seven different statistical methods to perform the reconstruction and these results were published online July 24, 2019 in the journal Nature Geoscience. The new 2,000-year reconstruction improves on previous efforts by using the most detailed and comprehensive database compiled by PAGES researchers. The dataset includes nearly 700 separate publicly available records from sources that contain indicators of past temperatures, such as long-lived trees, reef-building corals, ice cores, and marine and lake sediments. The data are sourced from all of Earth's continental regions and major ocean basins.
Graph shows global mean rates of temperature change over the last 2,000 years, as determined by a new reconstruction based on climate proxy data. Red denotes temperature increases while blue denotes temperature decreases. The green line shows the maximum expected warming rate without human influence; the dashed orange line signifies the ability of climate models to simulate this natural upper limit. The black line indicates average global as determined by direct measurements since the Industrial Revolution. Credit: University of Bern
By comparing the new reconstructions with existing climate simulations generated using the Coupled Model Intercomparison Project 5 (CMIP5) climate models, the PAGES research team was able to determine the relative contributions of several influences on global temperatures over time. These included natural influences, such as fluctuations in solar heating and the cooling effect of particles ejected by volcanic eruptions, as well as the human-caused influence of greenhouse gas emissions.
The results suggest that volcanic activity was responsible for variations before about 1850.Thereafter, greenhouse gases became the dominant influence on global climate. By removing these influences in their analysis, the researchers also identified the magnitude of the random changes that cannot be traced to a specific cause. The team's data-based reconstructions also agreed with model simulations when evaluating these random changes. This agreement between the researchers' data-based reconstructions and the CMIP5 simulations suggests that existing climate models can accurately predict future global temperature change over the next few decades. However, these simulations depend heavily on the choices that humans make in the future, which is very difficult to predict. According to the researchers, the uncertainty in the influence of human activities is not so large when looking forward only a few decades but in the longer term, the choices that are made regarding energy sources and how much carbon these sources emit will greatly matter.
Journal reference: Consistent multidecadal variability in global temperature reconstructions and simulations over the Common Era, Nature Geoscience (2019). DOI: 10.1038/s41561-019-0402-y
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© 2019 Oceanographer Daneeja Mawren
The World’s Largest Bloom of Seaweed is Devastating, and It May Very Well be Linked to Climate Change
A massive blossoming of seaweed is traversing the Atlantic Ocean, and it may be linked to changes in our climate.
The massive mat of seaweed, known specifically as Sargassum, stretches from the West African coast to the Gulf of Mexico—thousands of miles. This species of seaweed has been in the Atlantic for decades, although in sparse amounts. In 2011, however, researchers found this seaweed in exorbitant amounts, to which algae was connected in a continuous mat stretching across the ocean.
While this particular strand of seaweed provides a sanctuary for many species of fish, birds, and turtles, it can, in large amounts, devastate these same species. In 2011, when satellite imagery located the abnormal bloom of seaweed, researchers attributed it to discharge from the Amazon River during spring and summer. However, it was noted later on that upwelling off Africa during boreal winter may also be in play. The latter factor is likely caused by changes in Atlantic Ocean circulation patterns, courtesy of climate change.
The reason this strand of seaweed is rather devastating is because of where it happens to be washing up—popular tourist destinations across the Caribbean. The Yucatan Peninsula, home of Cancun, Playa del Carmen, and other prominent vacation hotspots have been particularly hard hit. Since the beginning of the year, over 650,000 tons of seaweed have washed ashore along the Yucatan’s coastline, and it comes with a distinct egg odor that has turned away many vacationers. The odor is caused by the release of hydrogen sulfide as the seaweed decomposes. Although some may be able to deal with the odor, the hydrogen sulfide has caused issues with local infrastructure, such as the corrosion of plumbing.
While Mexican officials have allocated funds to the cleanup and disposal of seaweed into dumps and the use of it as fertilizer for agriculture, researchers warn these extraordinary blooms of seaweed will become the new normal, and have even given the belt a name—the Great Atlantic Sargassum Belt.
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©2019 Weather Forecaster Jacob Dolinger
In a city already plagued by constant flooding and storm surge, climate change is a clear problem facing New Orleans. Located next to the southern tip of Louisiana, the Crescent City’s unstable ground and exceedingly low sea level have placed it in a zone ripe for encroaching seas. On top of that, hurricanes that form as a direct consequence of the warm waters of the Gulf of Mexico frequently bombard Louisiana, and this will only get worse as the global temperature continues to rise. This begs the question: How will New Orleans survive?
In response to this question, the U.S. government has tried to prepare the coastal city for increasingly pervasive storm surge by installing storm surge countermeasures through the United States Army Corp of Engineers (USACE). These countermeasures include, but are not limited to, levees, sea walls, and pumps. Such provisions can also be found in other vulnerable coastal cities around the world, such as Shanghai, Jakarta, and London. Unfortunately, New Orleans has had difficulty utilizing their defenses in the past.
When Hurricane Katrina hit Louisiana in 2005, it absolutely overwhelmed the flooding countermeasures put in place by the USACE. In fact, the flooding countermeasures were so ineffective that the levees themselves are often cited as the main reason why New Orleans flooded to the degree it did. The levees, canals, and floodwalls were annihilated by storm surge, allowing waters from nearby lakes and the Gulf of Mexico to invade the city. To make matters worse, it was revealed a year later that some of the pumps installed to get rid of floodwaters were defective. The storm surge was so monstrous that a large amount of buildings were completely unusable until they were pumped and rebuilt. This tragic fate could be indicative of the future of New Orleans.
Thankfully, there might still be hope for this important cultural and economic center. Lessons learned from Hurricane Katrina have better prepared the engineers, scientists, and officials for future disasters. Better designed levees, higher floodwalls that can stop up to 20 feet of storm surge, and warier city officials make it less likely that New Orleans will experience a Katrina-like failure again. However, it’s probable that these improvements won’t entirely save New Orleans from disastrous flooding in the future. Despite valiant efforts from engineers and officials, the city’s geography often leaves it defenseless from storm surge. As a result, there may be no way to completely erase the threat of storm surge from happening in New Orleans, especially with the intensifying climate. Regardless, the officials of New Orleans and the U.S. government must remain vigilant to protect this invaluable city from disaster. Hopefully, scientists and engineers will discover new ways to fight storm surge that will allow for more coastal security. Until then, it’s wise to remain watchful of incoming disasters that could devastate New Orleans and cities like it to minimize loss of life and property.
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© 2019 Weather Forecaster Cole Bristow