2010-10-25 01:43:01Hockey stick or hockey league?
John Cook

john@skepticalscience...
124.186.160.198

New blog post. Tossing up whether to go the Joe Romm carpet bombing approach and throw a whole bunch of hockey sticks in there - coral dC13, underwater hockey stick, South American hockey stick, Arctic hockey stick, spaghetti graph - or just go simple (I liked the idea of making all the graphs match in style and shape). Thoughts on my final conclusion welcome too. Thanks!


When most people refer to the 'hockey stick', they refer to its earliest incarnation - a temperature proxy by Mann, Bradley and Hughes created back in 1998. But in the climate change experienced over the last 1000 years, there are many hockey sticks. The amount of carbon dioxide being emitted by humans, mostly through the burning over fossil fuels, has a distinct hockey stick shape when viewed over the last 1000 years.

Figure 1: Fossil fuel emissions in million metric tonnes of carbon (CDIAC).

Our dramatic increase in carbon dioxide emissions has coincided with a dramatic increase in the amount of carbon dioxide in the atmosphere. CO2 levels have risen around 40% since pre-industrial levels and currently sit at around 390 parts per million, a level unseen for at least 15 million years.

Figure 2: Atmospheric CO2 concentration. (Green Line - Law Dome, East Antarctica and Blue line - Mauna Loa, Hawaii)

There are various drivers of climate - changes in solar output, aerosol levels in the atmosphere and the amount of carbon dioxide are the major drivers of long-term climate change over the last 1000 years. When we combine the net effect of sun, aerosols and carbon dioxide, we get the following shape in net climate forcing over the last 1000 years:

Figure 3: Combined radiative forcing from solar variations, carbon dioxide and aerosols - volcanoes are omitted (Crowley 2000).

Climate forcing essentially means changes in the planet's energy balance. Positive forcing means our climate is building up heat. When the planet builds up heat, it gets warmer. Consequently, we see the following shape in Northern Hemisphere land temperature:

Figure 4: Northern hemisphere temperature reconstruction from Moberg et al 2005 plus instrumental measurements of northern hemisphere land temperature (CRUTemp).

The original hockey stick by Mann, Bradley and Hughes didn't prove that humans are causing global warming. The evidence for man-made global warming lies in the multiple human fingerprints found throughout climate change. But the variety of hockey sticks (or hockey league) do tell a story. They tell the story of human activity causing a profound disturbance to our climate system.

People are often more affected by a story than by dry, scientific evidence. Perhaps that's why there has been so much vehement opposition to Mann's hockey stick, even while the science has moved on over the subsequent decade. But to say "the hockey stick is broken" is to ignore the full body of evidence of hockey stick shapes throughout climate change.

 

2010-10-25 02:12:53
nealjking

nealjking@gmail...
84.151.35.28

John,

In the last graph, you don't explain why the red graph appears at the end. Isn't this where knowledgeable naysayers will chorus, "Hiding the decline!"? You need to deal with this.

2010-10-25 02:28:59comment
Robert Way

robert_way19@hotmail...
142.162.11.6
John, mention those are 5-year averages in the last figure
2010-10-25 06:41:03
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.148.139

Explaining why the instrumental record is tacked on the end of Moberg's graph will provide a distraction, and disrupt the flow of the post. Maybe better to provide a link to the explanation elsewhere at Sks.

I was also wondering whether the spread of temperature confined species, away from the equator and up hillsides, would also show up as a hockey stick?. Not that I've read much about it apart from the Parmesan? paper.

 

2010-10-25 07:02:17
nealjking

nealjking@gmail...
84.151.35.28

Dappledwater,

 Which is the Parmesan paper?

 

 

2010-10-25 11:44:08
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.148.139

Neal, 

A globally coherent fingerprint of climate change impacts across natural systems 

And a review here:

Ecological and Evolutionary Responses to Recent Climate Change

Not a topic I've researched that much, hence the question above.

2010-10-25 13:57:57No dice with Parmesan
John Cook

john@skepticalscience...
124.186.160.198
No hockey sticks or long time series in the Parmesan paper - it's more a snapshot in time.
2010-10-25 17:09:03
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.130.39

John, I wasn't suggesting a hockey-stick in the Parmesan paper. What I was getting at was, is there some metric in the ecological shifts that could be used as such?.   

Anyway, ocean ph should also follow the trend in atmospheric CO2 i.e. it's a hockey-stick.