Warmer oceans likely prevent global droughts

As I’ve reported in many articles, sea-surface temperatures have been warming in recent decades. This warming may be linked to extreme weather conditions across the globe. However, this trend of shifting ocean temperature patterns simultaneously could be acting as a natural phenomenon to prevent planet-wide agricultural catastrophes.

A recent study in ScienceDaily indicates that analyzing global climate records from 1901 to 2020 discovered that shifting oscillations, such as El Nino and La Nina, create regional drought hotspots rather than allowing massive, simultaneous dry spells across the globe. Synchronized droughts generally affect only 1.8% to 6.5% of global land at any one time, protecting overall food supplies from compounding continental crop failures.

The world's oceans play a vital role in regulating Earth's climate and helping protect the planet from widespread, simultaneous drought. Covering approximately 71% of the Earth's surface, the oceans act as a massive reservoir of heat and moisture that continuously fuels the global water cycle. Although severe droughts can occur in many regions at the same time, ocean temperatures and circulation patterns help redistribute heat and precipitation around the globe, making a prolonged worldwide drought highly unlikely.

Severe summer droughts this season have been experienced across about half of Europe. The massive and destructive wildfires in this part of the world have been the result of extreme dryness and a very hot summer, especially in France and Spain. Low water levels are currently disrupting shipping, farming and other industries. One of Europe’s largest rivers, the Danube, has dropped to record low levels due to prolonged drought.

In the U.S., approximately 70% of the country is experiencing very dry to extreme drought. According to the latest U.S. Drought Monitor, the Spokane and Coeur d’Alene region is currently classified as having “severe drought” conditions. Many reports indicate that the southwestern U.S. is still in the middle of a “mega drought” that began in 2000. The overall period of dryness has led to the declaration of a water shortage at Lake Mead, which is the largest reservoir in the United States. With the intensifying El Nino, there is a better than 50/50 chance that heavier amounts of rainfall will fall across this region by late in the year.

Despite large areas of drought in the world, new studies show that the oceans shield the planet from global drought through evaporation. As the Sun warms the ocean surface, vast amounts of water evaporate into the atmosphere. This water vapor later condenses into clouds and eventually falls as precipitation, creating an overwhelming majority of the moisture that sustains Earth's precipitation. Without this continual supply of atmospheric moisture, much of the world's land would become much drier and less capable of supporting ecosystems and agriculture.

Ocean temperatures also influence major climate patterns that determine where rain falls. As mentioned earlier, the best-known example is the El Niño-Southern Oscillation (ENSO), a natural cycle involving changes in sea surface temperatures across the tropical Pacific Ocean. During an El Niño event, such as the current one, unusually warm Pacific waters eventually shift rainfall patterns around the globe, bringing wetter conditions to some regions while causing drought in others. La Niña, characterized by cooler Pacific waters, generally produces the opposite effects. Although these events can trigger devastating regional droughts, they rarely create drought everywhere simultaneously because atmospheric circulation redistributes moisture to other parts of the world.

As overall ocean temperatures rise, evaporation generally increases because warmer water releases more moisture into the atmosphere. Scientists estimate that the atmosphere can hold about 7% more water vapor for every 1.8 F increase in temperature. This additional moisture helps the global water cycle and can contribute to heavier rainfall events. However, increased ocean warmth does not eliminate drought. Recently, there have been intensifying contrasts between wet and dry regions. For example, while some areas experience more frequent flooding, others face longer and more severe droughts due to shifting atmospheric circulation and changing storm tracks.

However, oceans cannot completely prevent widespread drought if atmospheric circulation patterns shift dramatically or alters regional precipitation patterns. Instead, ocean temperatures tend to redistribute rainfall rather than eliminate drought, helping ensure that while some areas suffer water shortages, others receive above-normal precipitation.

In terms of our local weather, the very dry weather pattern continues across the Inland Northwest. Wildfires have recently erupted across eastern Washington, especially around Spokane, resulting in widespread evacuations and worsening air quality. Only 0.01 inches of rain was measured at Cliff’s station in July with no measurable moisture at the Spokane International Airport. Since June 1, only 0.25 inches of rain has fallen in Coeur d’Alene, compared to a two-month normal of 2.85 inches (1.93 inch normal for June and 0.92 normal for July).

With a strong high pressure system dominating most of the western U.S., very little moisture, if any, is expected in the region through at least the middle of August. Eventually, the new El Nino may bring some rainfall to the region by either late August or September. Stay tuned.

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Contact Randy Mann at [email protected].