West Coast climate more affected by ocean than by air

 Malibu Beach, California

Changing Winds Explain Most Pacific Coast Warming 
[Via SFCC]

Changes in winds over the eastern Pacific Ocean explain most of the warming trend along the West Coast of North America in the last century, according to a new analysis published in the Proceedings of the National Academy of Sciences.

Similar atmospheric shifts are known to drive fluctuations in Pacific climate over decades in the form of the Pacific Decadal Oscillation (PDO), a long-recognized pattern of seesawing ocean temperatures. The new research indicates that similar changes in regional pressure and winds can also drive trends in sea surface and coastal air temperatures that extend over a century or more.

This study used independently measured ocean and land-surface air temperature records from 1900 to 2012 to confirm an already well-documented increase of approximately 0.5 to 1 degree Celsius in the northeast Pacific Ocean and nearby land areas. What’s especially interesting and new about this work is that independently measured atmospheric sea level pressures over the past century show that circulation changes account for nearly all of the year to year, decade to decade, and century long surface temperature changes in the northeast Pacific Ocean and West Coast states since 1900.

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A nice discussion from the authors of their research all over the news about West Coast warming. Here is the relevant graph:

ocean

First, you do not see the same sort of temperature trend for West Coast temperatures as seen globally. One of the benefits of living on a coast – the oceans modulate the temperatures. As shown in this paper. This is not new and has been known for some time.

What is new is that almost all of this can be modeled using ocean-driven winds, not by direct impacts of greenhouse gas emissions into the atmosphere.

It has been known for a long time that coastal temperatures have not risen as rapidly an interior temperatures. The question was, was any effect due to direct emissions of greenhouse gases? The model the authors present indicate that West Coast air temperature change fits best with changing wind patterns than with CO2 release.

As the authors state:

This study used independently measured ocean and land-surface air temperature records from 1900 to 2012 to confirm an already well-documented increase of approximately 0.5 to 1 degree Celsius in the northeast Pacific Ocean and nearby land areas. What’s especially interesting and new about this work is that independently measured atmospheric sea level pressures over the past century show that circulation changes account for nearly all of the year to year, decade to decade, and century long surface temperature changes in the northeast Pacific Ocean and West Coast states since 1900.

Changes in winds explain most of the temperature differences, most of which took place before 1940. And the winds are determined by ocean currents and ocean temperatures. 

They make the point that regional variation is not the same as global. While at a global level, we can see changes, at more granular levels, such as regions, other factors can dominate. It is not surprising that being near an ocean can ameliorate temperature changes since this is one reason people like living near oceans – it is not nearly as hot or as cold as living inland.

So, the change in wind patterns explains most of the atmospheric temperature variability for parts of the West Coast. But what is causing the wind patterns to change? As the authors state:

This study shows that atmospheric circulation changes, essentially changes in winds, were the proximate cause for West Coast/NE Pacific temperature changes from 1900 to 2012. If anthropogenic effects were important for NE Pacific / west coast warming from 1900 to 2012, they likely occurred through an indirect circulation pathway that that is not well simulated by current global climate models. The more we understand the regional climate dynamics discussed in this research the better we can understand how they may interact with human-caused climate change, and what the combined effect on the region’s climate may be.

Indirect pathways in ocean circulation  are what we would expect from anthropogenic release of CO2 into the atmosphere. We are not putting the CO2 or heat directly into the ocean. We do know that the ocean is soaking up a lot of atmospheric heat. 90% of the additional heat is being stored in the oceans.

This will likely have an effect on ocean circulation and thus atmospheric properties, but an indirect one rather than the direct effect.

Getting a better idea of the effects on ocean circulation patterns will help inform us a lot, not only at the regional level but at the global.

We really do not have a great idea of all the drivers behind these ocean changes (such as El Nino or the Pacific Decadal Oscillation), although we are gaining a better understanding all the time.The oceans are the greatest heat sink we have but since we do not live there, we do not have as much data as we have with atmospheric data. 

Understanding this as fast as possible will make for better models. That is what science does.