A North Atlantic nasty surprise: AMOC slowing faster than expected

Atlantic Meridional Overturning Circulation slowing much faster than expected

It seems that the 2004 Hollywood blockbuster disaster movie The Day after Tommorrow, while highly exaggerated, had the seed of scientific fact based upon the possible disruption that could occur from the slowdown or catastrophic cessation of the Atlantic ocean Meridional Overturning Circulation (AMOC), also known as the thermohaline circulation or Great ocean conveyor belt.

A new study by Rahmstorf et al (2015) published in Nature Climate Change has found evidence for a slowdown of the overturning circulation. This is based upon multiple lines of observation suggesting that over recent decades the current system has been weaker than ever before in the last century, or even in the last millennium.

The Gulf Stream is part of this circulation system with warm waters, which are naturally lighter, flowing north, and responsible for the mild climate of north western Europe. In the sub-polar region these waters cool, become more dense, and sink to the bottom before they start flowing south along the ocean bottom towards the tropics, then the South Atlantic and the Southern Ocean. The conveyor belt of currents connects the Atlantic, Indian, Pacific and Southern Oceans providing heat transfer and mixing throughout the globe.

Related Links: What’s going on in the North Atlantic? at Realclimate Blog | New Research Shows Exceptional Slowdown In Major Atlantic Ocean Currents Greg Laden's Science Blog

Severe Tropical Cyclone Pam devastates Vanuatu and other Pacific Island nations

Tropical Cyclone Pam, a category 5 storm as measured on both the Australian and Saffir-Simpson storm measurement scales, with wind gusts over 300km/hr, has devastated the Pacific Island Nation of Vanuatu.

The storm made a direct hit on the capital Port Vila of this island country on Friday night and the early hours of Saturday morning, causing widespread damage, blocking roads, power and communication outages and destroying many homes and buildings. Even the main Hospital in Port Vila suffered damage.

Tom Skirrow from Save The Children says 10,000 people need emergency shelter in Port Vila alone according to Liam Fox, an ABC News Pacific Affairs Reporter. According to Radio New Zealand (@RNZNews) Vanuatu's Disaster Management Office says part of the country's main hospital, Vila Central, have been destroyed. This has been confirmed by Vanuatu's lands minister, Ralph Regenvanu, saing only one ward of Vila Central Hospital is still operational.

The United Nations Relief web reported:

The cyclone was one of the strongest ever recorded in the Pacific Islands with sustained winds of 270km/hr gusting to 360km/hr. The United Nations has stated that Pam could be one of the worst natural disasters in the history of the Pacific. Vanuatu’s President, Baldwin Lonsdale, has appealed to the global community for help. Thousands of people are in temporary shelters. Entire communities were severely damaged in some areas. Islands in the north and south of Vanuatu were hit most directly.

Unprecedented acceleration in the rate of temperature change coming up

The latest research published in Nature Climate Change based on CMIP5 climate modelling, argues that we are likely to see rapid rates of temperature rise in the near term of the next 40 year period that is unprecedented in the last 2,000 years. The rate of temperature increase is likely to rise to 0.25 ± 0.05 °C per decade by 2020. Much of this rise will be disproportionately felt in the northern hemisphere regions of the Arctic, North America and Europe.

This acceleration will occurr over the next 40 years despite what efforts we make to reduce our emissions. What mitigation action we do take will affect the rate of temperature rise after this near term period.

"We focused on changes over 40-year periods, which is similar to the lifetime of houses and human-built infrastructure such as buildings and roads," said lead author Steven Smith. "In the near term, we're going to have to adapt to these changes."

Hang onto your hats and sunscreen because this is going to become a wild ride in learning to adapt to extreme weather, especially heatwaves.

Taking the earth's temperature and the influence of ocean sea surface temperature cycles

I had a go at charting the global mean temperature trend. An interesting thing to do as it gives you an insight into all those global mean temperature graphs you see.

I started off with the GISS temperature anomaly dataset that goes from 1880 up to the present. The temperature anomaly data is provided in monthly intervals based upon a 1951-1980 baseline of 14.0 deg-C, but I really only used the data from 1970 to the present.

Using monthly data you see the extremes that sometimes occurr, both on the warm side and the cold side. I added a 12 month running average trend line (red) and a 5 year running average trendline (dark blue) to make the temperature trend clearer.

Here is the result: