CCS Week 3 - We Are Changing The Climate

This week we focus on signs and effects of anthropogenic climate change.

3.1 Signs of climate change

Measuring temperature at sea: past: temp read via thermometer in bucket of water brought up on deck today:

at the surface, temp read via thermometer of water brought into engine as coolant
at depth, by sensors on remote controlled submaines

Measuring temperature on land:

thermometers inside Stevenson Screens, which shield from direct radiation and rainfall (which could skew measurements and damage sensors)
Temps measured and predicted in shade.

3D temperature maps:

balloons held in the upper atmosphere allow temperature readings from altitude. This enables 3D climate map production.

Key indicators:

global mean surface temperature
- averaged over all sites
- urbanisation accounted for (i.e. urban areas have higher, steadier temperatures, which would otherwise skew surface means)
- usually presented relative to an average mean value (often from 1950-1980, allowing for presentation of older data to show below the avarage and modern data to show above)
- shows a clear upward trend over the past 3 - 5 decades, with the past three each measuring hotter than the preceeding one
global mean ocean temperature
- roughly follows same, rising, pattern seen in land temperature data
sea level changes
- steady rise over past century, constant gradient rather than “hockey stick”
- other studies explain half the rise due to thermal expansion (what is this?) and half due to melting land ice from Greenland and other smaller glaciers
- antartica remains cooler and does not contribute to rising sea levels (although it appears to break up more in recent years)
- melting sea ice does not contribute to rising sea levels, as the initial ice displaces the same volume of water as melting produces)
arctic ice extension
- over the past four decades, the arctic sea ice has reached lesser extents. In the past three decades, the ice has lost about half its area (nearly 40,000km³ down to a shade over 20,000km³ according to this graph: https://twitter.com/unfccc/status/831760914462420992)
extreme weather events: many people have the perception of weather changes during the past few years, in particular an increase in “extreme” weather events like floods, hurricanes and tornados. At preasent science cannot determin if anthropogenic forcing accounts for the events. Rising population means more people get affected by these extreme events.

Poll Questions:

Have you witnessed any signs of climate change?

The signs in the UK seem sublter than other areas. The boundaries between seasons have softened. Summers have shorter periods at the upper temperature range, with earlier or later peaks than I remember from the ’80s & ’90s. Winters feel less cold, with less snow but they have carried on longer. Some areas of the UK have seen significant flooding beyond what they were used to: even some cities have become blocked off by floodwaters (Lancaster 2015).

We see news reports of wilder weather conditions around the world. It seems hard NOT to attribute this in some way to climate change.

Which of the following signs of Climate Change do you think has the biggest global impact?

I answered as “sea level rise”. I suspect the increased quantity of water will have subtle and powerful effects on climate, driving other systems’ changes. Water absorbs and holds a lot of heat and so increasing the amount of water will likely change the way heat interacts with other climate features over the course of a year.

The impact of sea level rise on human life will be significant. Humans like to congregate at coasts and especially esturies. Low-laying areas may flood; villages and towns may need to expand inland or move entirely, potentially faster than citizens can manage. In many countries the costs will be prohibitive. The news is peppered with discussion of projected “climate refugees” already.

3.2 How has climate changed?

The course material linked to a Met Office website showing summaries and bulletins concernate climate changes over past years, and also explanations of terms and processes.

In crude summary, the site showed global mean surface temperatures have increased steadily since 1850 and dramatically over the past three decades.

3.3 State of the climate: extreme events

The NOAA Extreme Climate Events website describes two extremes “nearby” the UK, from 2015 data:

Europe, as a whole, experienced its second warmest year on record, behind 2014. Spain, Switzerland, Belarus, Lithuania, and Finland were each record warm.
Marrakesh, Morocco, received over 16 times its monthly average rainfall for August.

Asked to comment on whether these events contribute to evidence for climate change, I feel that on their own they contribute only a little to the argument. Read as discrete cases, they could represent individual annomolies. Furthermore, the context of the site and presentation of the data creates a mode of communication which forces the reader to view all the data as discrete anomolies.

However, the site groups these events by year. Viewing reports for close regions year by year begins to suggest identifiable trends. For example, looking across the set of data for Europe and the UK suggests a noticable shift in climate:

2000 wettest year for UK
2003 Significant heatwave in SW Europe (France, Spain)
2006 warmest year for UK
2006 warmest year for Norway
2011 2nd warmest year for UK
2011 Another SW European heatwave
2011 Summer months in Germany averaged 4˚C higher than average, 2nd warmest on record
2011 Norway’s wettest spring and 2nd wettest summer on record (since 1900), with flooding & landslides. Also warmest year.
2011 Finland had 2nd warmest year on record (although lack of information about warmest year lowers the impact of this annomolly)
2012 2nd wettest year for UK, with an unusually dry January, february & march
2012 Unusually warm across the whole of Europe, leading to drought and wildfires
2013 brought the UK very unusual weather: “coldest March and May since 1962 and 1996, respectively. Overall, spring was the coldest since 1962. Northern parts of the nation received almost 8 inches (20 cm) of snow from March 22–24—the region’s most significant late winter snow event since 1979”
2013 Spring in France fell 2˚C below average
2013 Some areas of Norway experienced 3x to 4x the typical precipitation
2014 Warmest recorded year in Europe, with over 20 countries experiencing record high temperatures
2015 2nd warmest year for Europe overall with some countries experiencing their warmest recorded averages

Antarctic sea-ice reached its largest maximum extent in 2012. Can you explain this in a warming world?

Whilst records for the northern hemisphere show significant warming trends, Antarctica seems to be experiencing the reverse.

The National Snow & Ice Centre at UofCol Boulder suggests that interactions between warmed sea water surrounding Antarctica and the cold air above it leads to stronger than usual winds. These predomenently south-westerly winds blow harder and faster than usual, conducting increasing amounts of heat away from the ice. This lowers ice temperatures, permittting the formation of more ice (I presume from the surrounding sea).

Experiencially I find it easy to intuit a cooling wind effect (blow on your skin or stand outside on a windy day to feel the effect). At school, I learned a little about the interaction of sea temperatures and air over neighbouring land: seas warm and cool slower than neighbouring land and as a result, air pressure differentials change direction as one warms and the other cools. I don’t understand the process well enough and have not studied the data to be able to intuit the suggestion from NSIC.

(records started in 1910).