"The dead hand of the past clutches us by way of living people who are too frightened to accept change." Kim Stanley Robinson, Ministry for the Future
Ben Noll is a meteorologist at the Institute of Water and Atmospheric Research in New Zealand. He is responsible for monitoring the atmosphere's moisture content and discovered a record-setting pattern of increasing moisture. He found that April was the wettest month on record, and March was the wettest month on record.
That is not all. For eleven consecutive months, the Earth has experienced unprecedented heat temperatures. Last month, it was 1.58 Celsius warmer than the average, per Copernicus.
The ocean, the largest ecosystem on Earth, comprising seventy percent of the planet's surface area, has been the warmest recorded daily for the past thirteen months. Part of that warming can be attributed to El Nino, a natural climate cycle, as well as the greenhouse effect. The issue is that increasing water vapor is due to anthropogenic greenhouse gas emissions from burning fossil fuels.
But natural climate cycles can’t explain what’s growing beneath the sea’s surface. The amount of heat stored within the sea’s top 2 kilometers has been increasing for decades, says NOAA oceanographer Hosmay Lopez, also in Miami. And the rate of that growth is accelerating.
In a tweet, Ben Noll broke the news on why flooding is seemingly everywhere lately.
April 2024 was the moistest April on record for the planet 📈 A warmer world is a moister world: this is evidenced by a weather variable called "total column water" or "precipitable water", the total moisture amount in a column of air, from the ground all the way up to the top… pic.twitter.com/clvgun79or
This is wild: Global warming without global mean precipitation increase? "When GHG and aerosol forcings are combined ... the global mean precipitation increase due to GHG warming has, until recently, been completely masked by aerosol drying." More ⬇️https://t.co/uL7RqAjYiQpic.twitter.com/iA9iyiRUFC
The problem for humanity and other living things is not just the dangers of flooding, though the impact is enormous for agriculture critical to feeding eight billion people. This is a chilling warning of doom, considering that moisture content indicates wet bulb temperatures are also increasing and accelerating.
Water vapor is one of the most important elements of the climate system. A greenhouse gas, like carbon dioxide, it represents around 80 percent of total greenhouse gas mass in the atmosphere and 90 percent of greenhouse gas volume.
Water vapor and clouds account for 66 to 85 percent of the greenhouse effect, compared to a range of 9 to 26 percent for CO2. So why all the attention on carbon dioxide and its ilk? Is water vapor the real culprit causing global warming?
The answer is that water vapor is indeed responsible for a major portion of Earth’s warming over the past century and for projected future warming. However, water vapor is not the cause of this warming. This is a critical, if subtle, distinction between the role of greenhouse gases as either forcings or feedbacks. In this case, anthropogenic emissions of CO2, methane, and other gases are warming the Earth. This rising average temperature increases evaporation rates and atmospheric water vapor concentrations. Those, in turn, result in additional warming.
The Conversation, a Creative Commons site, shares valuable insight on water vapor as a greenhouse gas,
And it is. But not only because greenhouse gas emissions continue to rise. What we are also observing is the long-predicted water vapour feedback within the climate system.
Since the late 1800s, global average surface temperatures have increased by about 1.1°C, driven by human activities, most notably the burning of fossil fuels which adds greenhouse gases (carbon dioxide and methane) to the atmosphere.
As the atmosphere warms, it can hold more moisture in the form of water vapour, which is also a greenhouse gas. This in turn amplifies the warming caused by our emissions of other greenhouse gases.
Some people mistakenly believe water vapour is a driver of Earth’s current warming. But as I explain below, water vapour is part of Earth’s hydrological cycle and plays an important role in the natural greenhouse effect. Its rise is a consequence of the atmospheric warming caused by our emissions arising especially from burning fossil fuels.
Water vapour: the other greenhouse gas
For every degree Celsius in warming, the water-holding capacity of the atmosphere increases by about 7%. Record-high sea temperatures ensure there is more moisture (in the form of water vapour) in the atmosphere, by an estimated 5-15% compared to before the 1970s, when global temperature rise began in earnest.
Water vapour is a powerful greenhouse gas. Since the 1970s, its rise likely increased global heating by an amount comparable to that from rising carbon dioxide. We are now seeing the consequences.
In many ways, water vapour is the most important greenhouse gas as it makes Earth habitable. But human-induced climate change is primarily caused by increases in the long-lived greenhouse gases carbon dioxide, nitrous oxide, methane and chlorofluorocarbons (CFCs).
As a general rule, any molecule with three or more atoms is a greenhouse gas, owing to the way the atoms can vibrate and rotate within the molecule. A greenhouse gas absorbs and re-emits thermal (infrared) radiation and has a blanketing effect.
Clouds have a blanketing effect similar to that of greenhouse gases but they are also bright reflectors of solar radiation and act to cool the surface by day. In the current climate, for average all-sky conditions, water vapour is estimated to account for 50% of the total greenhouse effect, carbon dioxide 19%, ozone 4% and other gases 3%. Clouds make up about a quarter of the greenhouse effect.
Why is water vapour different?
The main greenhouse gases – carbon dioxide, methane, nitrous oxide and ozone – don’t condense and precipitate. Water vapour does, which means its lifetime in the atmosphere is much shorter, by orders of magnitude, compared to other greenhouse gases.
On average, water vapour only lasts nine days, while carbon dioxide stays in the atmosphere for centuries or even millennia, methane lasts for a decade or two and nitrous oxide a century. These gases serve as the backbone of atmospheric heating, and the resulting rise in temperature is what enables the observed increase in water vapour levels.
The rise in carbon dioxide doesn’t depend on weather. It comes primarily from the burning of fossil fuels. Atmospheric carbon dioxide has increased from pre-industrial levels of 280ppmv to 420ppmv (an increase of 50%) and about half of that increase has happened since 1985.
This accounts for about 75% of the anthropogenic heating from long-lived greenhouse gases. The rest of human-induced atmospheric warming mainly comes from methane and nitrous oxide, with offsets from pollution aerosols.
The extra heating from water vapour has been on a par with that from increased carbon dioxide since the 1970s.
Water vapour and the water cycle
Water vapour is the gaseous form of water and it exists naturally in the atmosphere. It is invisible to the naked eye, unlike clouds, which are composed of tiny water droplets or ice crystals large enough to scatter light and become visible.
The most common measure of water vapour in the atmosphere is relative humidity.
During heatwaves and warm conditions, this is what affects human comfort.
When we sweat, the evaporation of moisture from our skin has a cooling effect. But if the environment is too humid, then this no longer works and the body becomes sticky and uncomfortable.
This process is important for our planet, too, because about 70% of Earth’s surface is water, predominantly ocean. Extra heat generally goes into evaporating water. Plants also release water vapour through a process called transpiration (releasing it through tiny stomata in leaves as part of photosynthesis). The combined process is called evapotranspiration.
The moisture rises into the atmosphere as water vapour. Storms gather and concentrate the water vapour so that it can precipitate. As water vapour has an exponential dependence on temperature, it is highest in warm regions, such as the tropics and near the ground. Levels drop off at cold higher latitudes and altitudes.
The expansion and cooling of air as it rises creates clouds, rain and snow. This vigorous hydrological cycle means water vapour molecules only last a few days in the atmosphere.
Water is the air conditioner of the planet. It not only keeps the surface cooler (albeit at the expense of making it moister) but rain also washes a lot of pollution out of the atmosphere to everyone’s benefit.
Precipitation is vitally important. It nourishes vegetation and supports various ecosystems as long as the rate is moderate. But as the climate warms, higher moisture levels increase the potential for heavier rainfall and the risk of flooding.
Moreover, the latent energy that went into evaporation is returned to the atmosphere, adding to heating and causing air to rise, invigorating storms and making weather extremes greater and less manageable.
These changes mean that where it is not raining, drought and wildfire risk increase, but where it is raining, it pours.
Kevin Trenberth, Distinguished Scholar, NCAR; Affiliate Faculty, University of Auckland, Waipapa Taumata Rau
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Kevin Trenberth, Distinguished Scholar, NCAR; Affiliate Faculty, University of Auckland, Waipapa Taumata Rau
This article is republished from The Conversation under a Creative Commons license. Read the original article.