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Boost for efforts to reduce urban fossil fuel emissions - 16/01/2019

Better carbon emission measures will help cities work out how well they’re fighting against climate change, scientists say – and what impact government policies have.

Sampling greenhouses gases downwind from Auckland City - Mt Victoria, Devonport, Auckland. © Jocelyn Turnbull

Sampling greenhouses gases downwind from Auckland City - Mt Victoria, Devonport, Auckland. © Jocelyn Turnbull

Urban areas cover about three percent of the earth’s surface but account for about 70 percent of global fossil fuel derived carbon dioxide emissions.
 
Signatories to the Paris Agreement vowed to cut emissions by around 12 percent by 2030, so it is essential to find out how much major cities emit, and how effective their mitigation efforts are.
 
A world-first study led by radiocarbon scientist Jocelyn Turnbull of GNS Science has compared the three standard methods for estimating net emission figures – that is, total emissions less the amount absorbed by “carbon sinks” like trees and other vegetation.
 
In a paper published in the Environmental Science and Technology journal this month, Dr Turnbull and her co-authors found the three methods are largely consistent, which is good news.
 
“This gives a level of confidence that we didn’t have before, because it means each method can potentially be used as a stand-alone way for obtaining meaningful results,” Dr Turnbull said.
 
She added that using two or more of the methods would reduce uncertainties even further.
 
Dr Turnbull is involved in collaborative projects to assess emissions in Indianapolis, Paris, Boston, Melbourne, Washington DC and Auckland.
 
In Auckland, GNS Science is leading a pilot Auckland Carbon Emissions (ACE) study to develop a full carbon budget for Auckland City.
 
“The good news is Auckland’s carbon sink may be offsetting more than we first anticipated,” Dr Turnbull says.
 
“This will be one of the few studies in the world using very precise radiocarbon measurements to quantify an urban carbon budget.”
 
At present it is hard to say how government policies are influencing Auckland’s emission rates, because not enough detailed information is known.
 
The Auckland project will test a method of determining this, which will open the way for
permanent carbon emission measurements in other New Zealand cities.
 
This initial study will be expanded in 2019 as part of the CarbonWatch-NZ project which will use atmospheric measurements to determine the carbon budget for all of New Zealand. 
 
ACE and CarbonWatch-NZ are endorsed by the World Meteorological Organisation as a leading example of how atmospheric measurements are used to determine national and urban carbon budgets.
 
CarbonWatch-NZ is a collaboration between NIWA, GNS Science, Landcare and University of Waikato.