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About Climate Change & Global Warming
In the mid-2030s, every U.S. coast will experience rapidly increasing high-tide floods, when a lunar cycle will amplify rising sea levels caused by climate change.
High-tide floods – also called nuisance floods or sunny day floods – are already a familiar problem in many cities on the U.S. Atlantic and Gulf coasts. The National Oceanic and Atmospheric Administration (NOAA) reported a total of more than 600 such floods in 2019. Starting in the mid-2030s, however, the alignment of rising sea levels with a lunar cycle will cause coastal cities all around the U.S. to begin a decade of dramatic increases in flood numbers, according to the first study that takes into account all known oceanic and astronomical causes for floods.
Led by the members of the NASA Sea Level Change Science Team from the University of Hawaii, the new study shows that high tides will exceed known flooding thresholds around the country more often. What’s more, the floods will sometimes occur in clusters lasting a month or longer, depending on the positions of the Moon, Earth, and the Sun. When the Moon and Earth line up in specific ways with each other and the Sun, the resulting gravitational pull and the ocean’s corresponding response may leave city dwellers coping with floods every day or two.
What Is the Sun's Role in Climate Change?
From NASA's Global Climate Change Website
The Sun powers life on Earth; it helps keep the planet warm enough for us to survive. It also influences Earth’s climate: We know subtle changes in Earth’s orbit around the Sun are responsible for the comings and goings of the past ice ages. But the warming we’ve seen over the last few decades is too rapid to be linked to changes in Earth’s orbit, and too large to be caused by solar activity.
The Sun doesn’t always shine at perpetually the same level of brightness; it brightens and dims slightly, taking 11 years to complete one solar cycle. During each cycle, the Sun undergoes various changes in its activity and appearance. Levels of solar radiation go up or down, as does the amount of material the Sun ejects into space and the size and number of sunspots and solar flares. These changes have a variety of effects in space, in Earth’s atmosphere and on Earth’s surface.
The current solar cycle began January 4, 2008, and appears to be headed toward the lowest level of sunspot activity since accurate recordkeeping began in 1750. It’s expected to end sometime between now and late 2020. Scientists don’t yet know with confidence how strong the next solar cycle may be.
What Effect Do Solar Cycles Have on Earth’s Climate?
According to the United Nations’ Intergovernmental Panel on Climate Change (IPCC), the current scientific consensus is that long and short-term variations in solar activity play only a very small role in Earth’s climate. Warming from increased levels of human-produced greenhouse gases is actually many times stronger than any effects due to recent variations in solar activity.
For more than 40 years, satellites have observed the Sun's energy output, which has gone up or down by less than 0.1 percent during that period. Since 1750, the warming driven by greenhouse gases coming from the human burning of fossil fuels is over 50 times greater than the slight extra warming coming from the Sun itself over that same time interval.
NASA and France’s space agency Centre National d’Études Spatiales (CNES) started jointly flying satellite altimeters in the early 1990s, beginning a continuous space-based record of sea surface height with high accuracy and near-global coverage. That legacy continues with 2020 launch of the joint U.S.-
European Sentinel-6 Michael Freilich mission and its altimeter, which will provide scientists with an uninterrupted satellite record of sea level surpassing three decades. The mission is a partnership between NASA, NOAA, ESA (European Space Agency), the European Organisation for the Exploration of Meteorological Satellites, and CNES.
NASA sea level researchers have long worked to understand how Earth’s changing climate affects the ocean. Along with launching satellites that contribute data to the long global record of sea surface height, NASA-supported scientists look to understand the causes of sea level change globally and regionally.
Through testing and modeling they work to forecast how much coastal flooding U.S. communities will experience by the mid-2030s and provide an online visualization tool that enables the public to see how specific areas will be affected by sea level rise. Agencies at the federal, state, and local levels use NASA data to inform their plans on adapting to and mitigating the effects of sea level rise.
The above graph compares global surface temperature changes (red line) and the Sun's energy that Earth receives (yellow line) in watts (units of energy) per square meter since 1880. The lighter/thinner lines show the yearly levels while the heavier/thicker lines show the 11-year average trends. Eleven-year averages are used to reduce the year-to-year natural noise in the data, making the underlying trends more obvious.
The amount of solar energy that Earth receives has followed the Sun’s natural 11-year cycle of small ups and downs with no net increase since the 1950s. Over the same period, global temperature has risen markedly. It is therefore extremely unlikely that the Sun has caused the observed global temperature warming trend over the past half-century. Credit: NASA/JPL-Caltech
Satellites Help Scientists Track
Dramatic Wetlands Loss in
Researchers mapped land change in coastal Louisiana from 1984 to 2020. Basins that failed to build new soil, such as Terrebonne and Barataria, experienced the most land loss -- more than 180 square miles (466 square kilometers). Credit: Jensen et al. Journal of Geophysical Research: Biogeosciences
From Lake Pontchartrain to the Texas border, Louisiana has lost enough wetlands since the mid-1950s to cover the entire state of Rhode Island. Using a first-of-its-kind model, NASA-funded researchers quantified those wetlands losses at nearly 21 square miles (54 square kilometers) per year since the early 1980s.
In the new study, scientists used the NASA-U.S. Geological Survey Landsat satellite record to track shoreline changes across Louisiana from 1984 to 2020. Some of those wetlands were submerged by rising seas; others were disrupted by oil and gas infrastructure and hurricanes. But the primary driver of losses was coastal and river engineering, which can have positive or negative effects depending on how it is implemented.
Centimeter-by-centimeter, wetlands are built by the slow accumulation – accretion – of mineral sediment and organic material carried by rivers and streams. Accretion makes new soil and counters erosion, the sinking of land, and the rise of sea level.
Human intervention and engineering often hold back or divert the flow of sediments that naturally accrete to build and replenish wetlands. For instance, reinforced levees and thousands of miles of canals and excavated banks have isolated many wetlands from the Mississippi River and the network of streams that course through its delta like veins and capillaries. In a few cases, engineering projects have added sediment to delta areas and built new land.
By analyzing Landsat imagery with tools from cloud computing, the researchers developed a remote sensing model that focused on accretion or the lack of it. Basins that failed to build new soil, such as Terrebonne and Barataria, experienced the most land loss over the study period -- more than 180 square miles (466 square kilometers). Other areas gained ground, including 33.6 square miles (87 square kilometers) of new land in the Atchafalaya Basin and 43 square miles (112 square kilometers) in the area known as the “Bird’s Foot Delta” at the mouth of the Mississippi River.
“The Louisiana coastal system is highly engineered,” said Daniel Jensen, lead author and postdoctoral researcher at NASA’s Jet Propulsion Laboratory in Southern California. “But the fact that ground has been gained in some places indicates that, with enough restoration efforts to reintroduce fresh water supply and sediment, we could see some wetland recovery in the future.”
Understanding wetland dieback and recovery is critically important because the Mississippi River Delta, like many of the world’s deltas, drives local and national economies through farming, fisheries, tourism, and shipping. “For the 350 million people who live and farm on deltas around the world, coastal wetlands provide a key link in the food chain,” said JPL’s Marc Simard, principal investigator of NASA’s Delta-X mission and co-author of the paper.
In several airborne and field campaigns since 2016, the Delta-X research team has been studying the Mississippi River Delta, the seventh largest on Earth, using airborne sensing and field measurements of water, vegetation, and sediment changes in the face of rising sea level. The Landsat analysis builds on this airborne mission. Delta-X is part of NASA's Earth Venture Suborbital (EVS) program, managed at NASA's Langley Research Center in Hampton, Virginia.
The new model by Jensen and colleagues is the first to directly estimate soil accretion rates in coastal wetlands using satellite data. Working with ground-based accretion records from Louisiana’s Coastwide Reference Monitoring System, the scientists were able to estimate amounts of mineral sediment from water pixels in the Landsat imagery and organic material from the land pixels.
The researchers said their approach could be applied beyond Louisiana because wetland loss and resiliency is a global phenomenon. From the Great Lakes to the Nile Delta, the Amazon to Siberia, wetlands are found on every continent except Antarctica. And they are declining in most places. Wetlands were recently called some of the “most vulnerable, most threatened, most valuable, and most diverse” ecosystems on the planet, according to an international analysis co-authored by NASA researchers.
But they also said a new generation of spaceborne tools, such as synthetic aperture radar, can increasingly inform conservation policies on the ground. This is because satellites support near-continuous mapping of ecosystems at a scale and consistency that is nearly impossible through traditional surveys and field work.
The futures of our wetlands and coastal communities are intertwined with climate change, so sustainable management is critical. By storing decomposing plant matter in soil and roots, wetlands act as “blue carbon” sinks, preventing some greenhouse gases (carbon dioxide and methane) from escaping into the atmosphere. When vegetation dies, drowns, and fails to grow back, wetlands can no longer sequester (bury) carbon in soil and vegetation. At current rates of wetland loss in coastal Louisiana, carbon burial may have decreased 50% from 2013 estimates.
“Forty percent of the human population lives within a hundred kilometers of a coast,” Simard said. “It’s critical that we understand the processes that protect those lands and the livelihood of the people living there.”
Map of soil accretion in coastal Louisiana, showing higher buildup in parts of Atchafalaya and the “Bird’s Foot Delta,” where the Mississippi River system deposits mineral-rich sediment during flood periods. Credit: Jensen et al. Journal of Geophysical Research: Biogeosciences..