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Climate change

Clear signs of human influence in global warming

PUBLISHED : Sunday, 18 February, 2018, 10:19am
UPDATED : Sunday, 18 February, 2018, 9:33pm

I refer to the letter from Alan Crawley (“Claims of human links to climate change do not hold water”, February 4).

If Mr Crawley has been poring over the latest Intergovernmental Panel on Climate Change (IPCC) report so diligently, then he must have deliberately left out in his letter the following statement that says it all: “Human influence has been detected in the warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.”

Interested readers are referred to the Summary for Policymakers (Section D.3) of the IPCC Fifth Assessment Report and the underlying chapters, in particular, Chapter 10. Mr Crawley also distorted the message on the so-called “slowdown” in temperature rise.

Quoting from Chapter 1: “Even though the projections from the models were never intended to be predictions over such a short timescale, the observations through 2012 generally fall within the projections made in all past assessments.”

Typical of those suffering from denial syndrome, your correspondent seems to take comfort in the fact that 2017 is not as hot as 2015 and 2016.

According to the World Meteorological Organisation, 2017 is set to be among the top three hottest years, that is, the three hottest years on record, 2015, 2016 and 2017 – occurring in a row. The global average temperature for 2013-2017 is likely to be the highest five-year average on record.

The current rate of sea level rise is about 3.2mm/year (climate.nasa.gov/vital-signs/sea-level). The average rate of sea level rise during the satellite altimetry era is about twice the average during the 20th century, which is much higher than the average for the last two millennia (Chapter 5 of the IPCC’s assessment report).

Mr Crawley suggested the Paris Agreement would not change anything. His suggestion would certainly come true if “clear-thinking” people all think like him, instead of taking proactive action to reduce carbon emissions.

Lee Sai Ming, senior scientific officer, Hong Kong Observatory