The world's biggest hoax? Part 1

In future I’m going to have a look at specific, recent stories about climate change in the media, but I thought I’d write the first proper post here on arguably the biggest question surrounding anthropogenic (human-caused) climate change: is it really happening? This is a big topic so I’m going to split it into two posts.

The arguments against anthropogenic climate change come in several forms. Some deny that climate change is happening:

Snowing in Texas and Louisiana, record setting freezing temperatures throughout the country and beyond. Global warming is an expensive hoax!

— Donald J. Trump (@realDonaldTrump) January 29, 2014

Others, such as more than half the US Senate, recognise that the climate is changing but refute humanity’s role. Many point to past changes in both climate and CO₂ as evidence that current changes are natural or within ‘normal variation’, and deny that there is a scientific consensus regarding our role.

Meanwhile many media outlets regularly publish articles predicting the extreme and imminent effects of climate change, such as destroying infrastructure, worsening extreme weather events and even endangering US military operations. I hope to have a look at some of these in a later blog.

Much has been written for and against these arguments, and I can’t cover the nuances of every point in just one post. I would really recommend the Skeptical Science blog for a more detailed discussion of specific questions (thanks to Anson for the recommendation).

For now though, I will try to answer whether climate change is all a hoax by simplifying it to two key questions:

1) Does evidence support the idea that climate is changing outside the bounds of ‘normal variation’? (This post)
2) Does evidence support the idea that human activity has played a significant role in this change? (Next post)

Firstly, I’d like to share this awesome graphic from NASA. 

Figure 1: Surface temperature changes from 1880 to 2015, using a rolling five year average. Blue colours represent temperatures cooler than the 1951-80 baseline, while red colours represent temperatures above that baseline.

It seems pretty clear that temperatures have risen over the last century-and-a-bit.

Bloomberg plotted NOAA data to show a similar trend. They also highlighted the fact that 15 out of the 16 hottest years on record have been this century, and that 2015 was not only the hottest year on record, but also beat the previous record by a record margin (N.B. NASA’s data suggests the increase from 1997-8 was larger, but corroborates the fact that 2015 was the hottest year on record).

I’d say these data sources are fairly reliable. However, arguably the most reliable sources of data relating to climate change are the IPCC reports. 

Box 1: The IPCC The Intergovernmental Panel on Climate Change is Nobel Prize-winning body, established by the UN to improve understanding of the scientific basis of climate change. It doesn’t carry out its own research, but instead reviews published papers (both peer- reviewed and non peer-reviewed). Based on this evidence, it then reaches conclusions, and, most importantly and interestingly I think, attaches a degree of certainty to these. Although the IPCC has received much criticism in the past, for example over claims about the disappearance of Himalayan glaciers it is generally considered to give a fair reflection of the scientific consensus on climate change. The most recent report, its 5th, was published in 2013.

So what does the IPCC have to say about whether the climate is warming? In the most recent report it states that ‘the globally averaged combined land and ocean surface temperature data... show a warming of 0.85 [0.65 to 1.06]°C²⁰ over the period 1880 to 2012, for which multiple independently produced datasets exist’ (the figures in square brackets are the error margins). 

To me, this all seems fairly conclusive, but let’s look at one of the most popular arguments of climate change sceptics: ‘the great pause’. As the picture below demonstrates, it is a popular claim that temperatures have stopped increasing since the late 1990s.

Figure 2: The Sunday Mail’s headline and graph from October 2012.

As we saw above, warming hasn’t stopped in the last decades. The climate system is complex, and human impacts are modulated by and interact with natural cycles, such as El Niño events (which contributed to the highs in 1997/8 and 2015). We therefore don’t see a totally regular, noise-free pattern, but the short term variation does not negate the long term trend. In fact, a recent Nature paper found that hiatuses like this one are statistically inevitable when such small samples are considered.

However, even if we accept warming is occurring, this is only in the context of 130 years. We know the climate has fluctuated much more wildly in the past, with both ice ages and the sweltering conditions that accompanied the dinosaurs firmly in the public imagination. So why are modern changes any different? The IPCC states with high confidence that ‘1983 to 2012 was very likely the warmest 30-year period of the last 800 years in the Northern Hemisphere’ but this still barely registers on geological time scales. However, if we do look at a longer time scale, such as the Holocene (the last 11,000 years), it is easier to see the significance of recent changes. It is not the magnitude but the rate of warming that is alarming.

Figure 3: Adapted from Marcott et al. 2013 by www.realclimate.org. 

So far, so good (or bad for the inhabitants of planet Earth). But what about our role? Check out my next post to find out!