Climate and environment updates: Nearly 40% of the world's trees face extinction

The weather phenomenon responsible for the extreme rainfall and flooding in Valencia, Spain, isn't rare or even uncommon. It was also well forecasted in the days leading up to the storm.

The Mediterranean region, including parts of eastern Spain, is frequently affected by heavy rainfall and significant flash flooding events. This recent disaster saw a year's worth of rainfall in just eight hours. In September 2019, the same region saw 12 to 18 inches of rain in 48 hours.

What's responsible for these events is a weather system known as a cut-off low. This happens when a low-pressure area is separated from the primary airflow.

Cut-off lows are common and can happen at any time of the year, anywhere in the world. When there is an extended stretch of cloudy, damp, and dreary weather, this is often related to a cut-off low.

However, the slow-moving nature of a cut-off low can set the stage for devastating extreme rainfall events when it interacts with other favorable factors, like the warm waters of the Mediterranean Sea and nearby mountains. Because it is slow-moving, it can quickly pound areas with relentless rounds of heavy rain, resulting in significant flooding.

In Spain, these weather events are often called a "gota fría," which translates to "cold drop." But that term doesn't tell the whole story. What happened in Valencia wasn't caused by a sudden cold blast sweeping across the region but by the unique characteristics of a cut-off low.

That's not to say that cold air in the atmosphere doesn't play a role in enhancing the precipitation. It does bring more frequent rounds of heavy rain. As the system pushes the colder air over the very warm waters of the Mediterranean Sea, it helps trigger and enhance areas of heavy rain.

Because the low-pressure system moves very slowly, it keeps sending waves of heavy rain over the same areas for an extended period, bringing extreme rainfall totals and catastrophic flash flooding.

The nearby mountains also likely enhanced the precipitation and impacts. Plus, the infrastructure in the Valencia region, like many municipalities, isn't built to handle this amount of rainfall. Add in all of those factors, and you get catastrophic flash flooding.

What role, if any, does climate change play in these extreme weather events?

Climate attribution science will look at how much worse the rain was because of human-caused emissions, but we know that human-amplified climate change is supercharging the water cycle, bringing heavier rainfall and related flood risks. More intense extreme rainfall events increase the frequency and scale of flash flooding as the influx of water is more than the infrastructure of many municipalities was built to handle.

According to the U.S. Government's Fifth National Climate Assessment, human-amplified climate change is contributing to increases in the frequency and intensity of the heaviest precipitation events. So, in a way, we are all making it rain more.

-ABC News meteorologist Dan Peck and ABC News Climate Unit's Matthew Glasser

We waste a lot of food. According to the U.N., over a billion tons of it are wasted each year globally, most of it from households. Not only does wasting all this food cost the average American family $1,200 a year, but it's a significant source of greenhouse gas emissions.

The EPA says food waste in the U.S. is equivalent to the greenhouse gas emissions of more than 50 million passenger cars and is responsible for 58% of methane emissions from municipal landfills.

Methane is a particularly potent greenhouse gas because it traps more heat in the atmosphere than carbon dioxide. The U.N. Environment Programme says methane is "responsible for more than 35 percent of the global warming we are experiencing today."

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Tips for eliminating carbon emissions in your daily life 

ABC News chief meteorologist Ginger Zee shares tips for eliminating carbon emissions in your day-to-day life.

ABCNews.com

How does our food waste become methane?

Landfills act like big diaper linings on the ground, so nothing we throw away decomposes into the soil. There's a barrier preventing it. Our food waste gets sandwiched between all the plastic, metal and non-organic trash, and without oxygen, it mummifies and releases methane. So, every time we throw away leftover food, we create methane and speed up climate change.

There are, however, ways to curb food waste at home. Composting can turn leftovers into fertilizer for your plants and homegrown produce. If you don't have a garden, you can use a product like the Mill Kitchen Bin to turn your food waste into clean, dry grounds that don't smell. Those grounds can then be used as part of the composting process at home or given to a local community garden or farm.

The Too Good To Go app is another way of keeping food out of landfills. The service allows people to purchase surprise bags of surplus food from nearby restaurants, bakeries and grocery stores, preventing perfectly edible items from being thrown away. The bags, priced between $5 and $10, are packed with various items that are still good to eat but would have been thrown away.

Understanding food labels can also significantly reduce your waste. The often confusing terms "use by," "best by," and "expiration dates" sound similar but mean different things.

A "use by date" is the last date recommended for eating a product while it's still at its peak quality. After this date, the food might still be safe, but the quality may decline. For perishable items like dairy or meats, it's often best to follow this date closely, but use your nose and eyes to help determine whether it's still good.

"Best by" or "best before" dates are about the product's quality, not safety. It indicates when the food will be at its best flavor or texture. After this date, the food is usually still safe to eat, but it might not taste as good or have the same texture. Often, you won't even notice a difference.

"Expiration dates" are dates found on products where safety is a concern, like baby formula or certain medications. After this date, the product should not be consumed, as it may not be safe or effective.

-ABC News Chief Climate Correspondent Ginger Zee and ABC News Climate Unit's Matthew Glasser

Our planet is facing another unfortunate climate milestone.

According to a new report from the World Meteorological Organization (WMO), carbon dioxide concentrations have increased by more than 11% in just two decades, making 2023 a record for the amount of the greenhouse gas currently in our atmosphere.

The WMO says CO2 is now building up in the atmosphere faster than at any time in human existence. They say massive vegetation fires, which emit greenhouse gases, and El Niño, which can reduce our forests' ability to absorb CO2 due to drought, contributed to the recent surge. However, the U.N. agency also points out, "The reason behind this decade-long significant increase in CO2 is historically large fossil fuel CO2 emissions in the 2010s and 2020s."

The WMO began reporting on greenhouse gas emissions in 2006. That year, they found that atmospheric CO2 levels for 2004 were at 377.1 parts per million. Last year, they were recorded at 420 parts per million. That puts CO2 concentrations at 151% above the preindustrial era.

Methane, one of the worst greenhouse gases in terms of global warming, also reached a record level for atmospheric concentrations. It is now 265% higher than preindustrial readings at 1,934 parts per billion.

Because CO2 stays in the atmosphere for 300 to 1,000 years, according to NASA, the WMO is warning that these high levels of greenhouse gases "lock in future temperature increase" even if emissions are cut to net zero.

-ABC News Climate Unit's Matthew Glasser

It may be fall, but it feels a lot like summer in much of the country. That has some people wondering: Is climate change responsible for these record-high temperatures? With climate attribution science, we can now answer that question and determine when human-amplified climate change is responsible for extreme weather events and the significance of that impact.

Using advanced computer models, climate attribution science takes a real-world weather event, such as a record high-temperature day or a hurricane, and compares it to the world where human-caused, post-industrial greenhouse gas emissions don't exist. By comparing what is actually happening with what would have happened without human intervention, science can estimate how likely or severe a weather event has become due to climate change.

Climate Central, a nonprofit climate research and communications organization, uses climate attribution science to provide real-time data that shows "how much climate change influences the temperature on a particular day." The information is displayed on a global interactive map called the Climate Shift Index.

For example, the Index showed that human-amplified climate change made Sunday's record high in Tucson, Arizona of 98 degrees at least three times more likely. The same was true for Waco, Texas, which broke a record with 92-degree heat, and Mobile, Alabama, which hit a record 90 degrees.

Extreme heat is the deadliest weather-related hazard in the U.S., with children and adults over 65 being among the most vulnerable to heat-related illnesses and death. And the average number of heat waves that major U.S. cities experience each year has doubled since the 1980s, according to the federal government's Fifth National Climate Assessment.

-ABC News Climate Unit's Matthew Glasser