Fresh water cycles from ocean to air to clouds to rivers and back to oceans. This continuous shuttle can give us the illusion of certainty. Fresh water always comes from the tap. is not it?
Unfortunately, this is not guaranteed. Climate change It shifts as the water cycle deposits water on Earth, as dry areas continue to dry out, and wet areas become wetter.
our research Posted today in nature He discovered that the water cycle is changing faster than we thought, based on changes in our oceans.
This finding underscores the urgent need to end greenhouse gas emissions before the water cycle changes beyond recognition.
If this sounds dangerous, it is. Our ability to tap into fresh water makes modern society possible.
The water cycle has already changed
As the Earth warms, the water cycle begins to condense into “wet – wet – dry – dry – dry” pattern.
This means that more and more fresh water is leaving dry areas of the planet and ending up in wet areas.
How could this look? Weather intensification. In relatively dry areas, more severe droughts, more often. In relatively humid areas, storms and floods are more severe.
This shift is already happening. In its landmark 2021 Report, the United Nations’ Intergovernmental Panel on Climate Change (IPCC) drew on this growing body of research to conclude that climate change was indeed causing Long-term changes to the water cycle.
The changes we’re seeing are just the beginning. Over the next few decades, the intensification of the water cycle may make it difficult for people to obtain a reliable supply of fresh water across large areas of the planet.
Disturbingly, while we know the water cycle is condensing, we don’t quite know how much and how fast. This is where the ocean comes into play.
How to use the ocean as a rain gauge
The main reason why it is so difficult to measure changes in the water cycle directly is that we do not have sufficient measurements of rainfall and evaporation on our planet.
On a practical level, it is very difficult to set up permanent rain gauges or evaporation basins on 70 percent of our planet’s surface covered in water. Additionally, when we assess change over the long term, we need measurements from decades ago.
The solution that scientists have settled on is to use the ocean. Many may not realize that the ocean can be less or more saline depending on the area. For example, the Atlantic Ocean is saltier than the Pacific Ocean on average.
why? rain. When fresh water falls as rain into the ocean, it softens the sea water and makes it less salty. As the water evaporates from the surface, the salt is left behind, which leads to increased salinity.
This means that we can better use the recorded changes in ocean salinity as a kind of rain gauge to detect changes in the water cycle.
Previous research used this method to track changes in salinity at the ocean surface. This research suggested that the water cycle massively intensified.
Unfortunately, the ocean doesn’t stay constant like a traditional rain gauge. Currents, waves, and circular rotating currents keep ocean waters in constant motion. This uncertainty has left a question mark about how accurately the correlation between salinity and water-cycle change is in fact.
In response, we have developed new methods that enable us to accurately correlate changes in ocean salinity with changes in the portion of the water cycle that transports fresh water from warmer regions to colder regions.
Our estimates indicate how the broader water cycle is changing in the atmosphere, on land, and across our oceans.
What we found in our area New study? Fresh water equivalent to 123 times the water of Sydney Harbor has shifted from the tropics to colder regions since 1970. This is an estimated 46,000 to 77,000 cubic kilometers of water.
This corresponds to an intensification of the water cycle of up to 7 percent. This means up to 7 percent more rain in wetter areas and 7 percent less rain (or more evaporation) in dry areas.
This is at the high end of the ratings set by many Previous studiesindicating a condensation closer to 2-4 per cent.
Unfortunately, these findings suggest that potentially catastrophic changes in the water cycle may be approaching faster than previously thought.
What will the future look like with a changing water cycle?
If our water cycle is getting denser at a faster rate, that means more severe droughts and stronger and more frequent rainfall events.
Even if the world’s governments achieve their goal and keep global warming at 2, the IPCC predicts that we will still tolerate extreme events. An average of 14% stronger For the baseline period 1850-1900.
Some people and ecosystems will be affected more than others, as last year’s IPCC report made clear. For example, the Mediterranean countries, southwest and southeast Australia, and Central America will become drier, while the monsoon and polar regions will become wetter (or snowy).
In dry areas affected by these changes in the water cycle, we can expect to see real threats to the viability of cities unless alternatives such as desalination are put in place.
what should we do? You already know the answer.
Decades of scientific research has shown the very clear relationship between greenhouse gas emissions and rising global temperatures, which in turn intensify the water cycle.
This is another reason why we must move as quickly as possible in human terms toward net zero emissions to reduce the damage from climate change.
The changes in the water cycle that we observed were largely due to older emissions, from the mid-20th century and earlier. We’ve increased our emissions significantly since then.
What comes next is entirely up to us.
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