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Climate Variability vs AGW

August 28, 2019

Climate Variability vs AGW

Emissions of CO2 from burning fossil fuel contributes significantly to a gradual increase in the world’s average temperature.  What’s also known but less understood is the erratic variation in the average temperature due to cycles in the ocean, resulting in episodes of El Nino and La Nina.  Some claim that these temperature extremes are well-understood as a result of changes in the trade winds, as the wind pushes the water around the Pacific ocean, exposing colder or warmer water to the surface. This may have been a perfectly acceptable explanation, except it doesn’t address what causes the wind to vary — in other words the source of the erratic wind variation is just as unknown. 

So we are still left with no root cause for the ocean cycles. Apart from the strictly seasonal changes we have no explanation for the longer-term pattern of natural variation observed. 

The likely key to a physical understanding rests in solving the fluid dynamics of the ocean. There are two aspects to this that have long presented an intellectual challenge. The first challenge has been to model the sloshing dynamics of a huge body of water — this typically involves numerical calculation in the form of computational fluid dynamics (CFD). The second challenge is to feed in a possible forcing and see if that can match the cyclic patterns observed. This requires a search through plausible physical mechanisms. Complicating matters is that the cycles may be chaotic so that any agreement we find would be useless from a practical standpoint, as chaotic patterns are impossible to model regardless of the source forcing.

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Long-term climate variability ‘could fall’ as the world warms

February 9, 2018

Long-term climate variability ‘could fall’ as the world warms

Long-term climate variability is the range of temperatures and weather patterns experienced by the Earth over a scale of thousands of years. New research suggests it could fall as the world warms.

A study using data taken from fossils and ice cores finds that long-term temperature variability decreased four-fold from the Last Glacial Maximum (LGM) around 21,000 years ago to the start of the Holocene around 11,500 years ago. Within this period, natural processes caused the planet to warm by around 3-8C.

If future global emissions are not curbed, human-driven global warming could cause further large declines in long-term temperature variability, the lead author tells Carbon Brief, which may have far-reaching effects on the world’s seasons and weather.

However, it is still unclear how a decline in long-term variability could affect the frequency of extreme weather events, she adds. This is because the chances of an extreme event happening could be influenced by both short- and long-term climate variability, as well as global temperature rise.

Digging up the past

The new study, published in Nature, is the first to make a global assessment of how long-term temperature variability changed from the LGM to the Holocene.

During the LGM, the world’s last major ice age, snow covered much of Asia, Europe and North America. Yet, within a few thousand years, global temperatures rose by around 3-8C, causing the ice to thaw and the world to enter its current geological period, the Holocene.

The cause of this temperature rise is still disputed by scientists, but research suggests the natural release of large stores of CO2 from the world’s oceans may have played a role.

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February’s global temperature spike is a wake-up call

March 21, 2016

February’s global temperature spike is a wake-up call

Global temperatures for February showed a disturbing and unprecedented upward spike. It was 1.35℃ warmer than the average February during the usual baseline period of 1951-1980, according to NASA data.

This is the largest warm anomaly of any month since records began in 1880. It far exceeds the records set in 2014 and again in 2015 (the first year when the 1℃ mark was breached).

In the same month, Arctic sea ice cover reached its lowest February value ever recorded. And last year carbon dioxide concentration in our atmosphere increased by more than 3 parts per million, another record.

What is going on? Are we facing a climate emergency?

February temperatures from 1880 to 2016 from NASA GISS data. Values are deviations from the base period of 1951-1980. Stefan Rahmstorf

El Niño plus climate change

Two things are combining to produce the record warmth: the well-known global warming trend caused by our greenhouse gas emissions, and an El Niño in the tropical Pacific.

The record shows that global surface warming has always been overlaid by natural climate variability. The biggest single cause of this variability is the natural cycle between El Niño and La Niña conditions. The El Niño in 1998 was a record-breaker, but now we have one that looks even bigger by some measures.

The pattern of warmth in February shows typical signatures of both long-term global warming and El Niño. The latter is very evident in the tropics.

Further north, the pattern looks similar to other Februaries since the year 2000: particularly strong warming in the Arctic, Alaska, Canada and the northern Eurasian continent. Another notable feature is a cold blob in the northern Atlantic, which has been attributed to a slowdown in the Gulf Stream.

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