venice

Our cities are sinking

June 24, 2025 By EarthWise Leave a Comment

A new study by the Columbia University Climate School has found that all of the 28 most populous cities in the United States are sinking to some extent. This phenomenon of subsidence is not just taking place in cities on the coast, where relative sea level is an issue, but also in cities in the interior.

The primary cause of subsidence is large-scale groundwater extraction for human use. When water is withdrawn from aquifers made up of fine-grained sediments, the pore spaces formerly occupied by water can eventually collapse, leading to compaction below and sinkage at the surface.

The fastest sinking city in the US is Houston, with more than 40% of its area subsiding more than 5 millimeters a year and 12% sinking at twice that rate. Some local spots are going down as much as 5 centimeters a year. These seem like very small numbers but the fact that the subsidence is often not uniform across an urban area means that there are stresses to building foundations and other infrastructure. Parts of Las Vegas, Washington D.C., and San Francisco have particularly fast sinking zones.

There are other causes of subsidence. In Texas, pumping of oil and gas adds to the phenomenon. A 2023 study found that New York City’s more than one million buildings are pressing down on the Earth so hard that they may be contributing to the city’s ongoing subsidence. About 1% of the total area of the country’s 28 largest cities faces some danger from uneven subsidence.

Overall, some 34 million Americans live in cities affected by subsidence. Global cities facing especially rapid subsidence include Jakarta, Venice, and here in the U.S., New Orleans.

**********

Web Links

All of the Biggest U.S. Cities Are Sinking

Photo, posted December 27, 2012, courtesy of Katie Haugland Bowen via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Keeping Venice From Flooding | Earth Wise

January 6, 2022 By EarthWise Leave a Comment

Since 2003, Venice Italy has been building a system of mobile gates at three inlets to its famous lagoon. The project is called MOSE, the Italian word for Moses, but is actually an acronym for the Italian words meaning Experimental Electromechanical Module.

The 78 mobile gates are metal box structures that sit at the bottom of inlet channels. When a high tide is predicted, compressed air is pumped into the structures. The air causes the barriers to rise up to the surface and block the flow of the tide, thereby preventing water from flowing into the lagoon.

The system had an important test on November 3 when water levels were predicted to rise four-and-a-half feet above normal at high tide and strong winds were blowing. Water at that level is enough to flood 60% of the city, including the famous St. Mark’s Square, which is unfortunately the lowest part of the city.

Activating the flood gates proved to be successful. Even though high tide water levels in fact rose 4.3 feet in the surrounding Adriatic Sea, they only reached 2.7 feet in Venice, which was enough to prevent significant flooding.

Rising sea levels have led to increasingly frequent floods in Venice. In 2019, before the MOSE system was available for use, there were more than 25 high-water events swamping Venice, including one in November of that year that was the second worst on record.

Some researchers have calculated that the system will need to be closed for as much as 3 weeks a year by the end of the century even if emission reductions are reasonably effective. If they aren’t, the gates may be closed for at least two months a year by 2080.

After many years of delays, setbacks and controversies, the system is finally operational.

**********

Web Links

Venice Holds Back the Adriatic Sea

Photo, posted October 25, 2014, courtesy of Pedro Szekely via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Carbon From 25 Cities | Earth Wise

September 10, 2021 By EarthWise Leave a Comment

There are roughly 10,000 cities in the world, defined as places with at least 50,000 inhabitants with a sufficient population density. Roughly half the world’s population lives in cities.

Urban carbon emissions are one of the world’s biggest problems with respect to the climate. A new study has determined that just 25 cities globally are responsible for 52% of urban greenhouse gas emissions.

The study gathered data on greenhouse gas emissions in 167 cities in 53 countries. The results were that megacities in Asia, such as Shanghai and Tokyo, were among the biggest total emitters, and that major cities in Europe, the US, and Australia tended to have larger per capita emissions. Several Chinese cities, however, matched levels seen in developed countries. Researchers tracked emissions over time in 42 of the cities studied. Some cities saw declining emissions in the period between 2005 and 2016. These included Oslo, Houston, Seattle, and Bogota. Others saw large increases, including Rio de Janeiro, Johannesburg, and Venice.

The largest sources of emissions are power generation, industry, and transportation. In a third of the cities, road transportation alone accounted for over 30% of emissions. (Railways, waterways, and aviation combined only accounted for less than 15% of total emissions).

Half of the world’s population lives in cities, but cities are responsible for more than 70% of greenhouse gas emissions. Thus, cities have a big responsibility for the decarbonization of the global economy. Of the 167 cities in the study, 113 have set emission-reduction targets. But as the study shows, cities have much more work to do to meet the goals of the Paris Climate Agreement.

**********

Web Links

Two Dozen Large Cities Produce 52 Percent of Urban Carbon Emissions

Photo, posted December 1, 2017, courtesy of Hector Galbis via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Saving Venice From The Sea

January 26, 2018 By EarthWise Leave a Comment

The risks of rising sea waters are growing more apparent every year. While the world struggles with taking action to reduce the carbon emissions that are driving the sea level rise, cities around the world are building sea walls designed to protect them from storm surges and flooding. Most of these are massive, complex infrastructure projects that cost billions of dollars and take decades to complete.