Arguments
Can humans affect global climate?
Posted on 26 August 2010 by John Russell
When we experience weather events like hurricanes and floods, it’s very easy for us to feel insignificant and powerless in the face of such massive natural forces. How can humans influence this? Well, yes, we can. Of course we can’t influence a single weather event, but we can and do have a long term influence on the climate that causes it.
Since the industrial revolution, with ever-increasing supplies of fossil fuels, the activities of a dramatically expanding world population have made significant alterations to the make-up of our atmosphere.
In some cases human-caused change is direct and unambiguous. The harmful effect of the human release of CFCs on the ozone layer is well documented and not disputed. Down on the ground, draining of marshland and deforestation can produce a significant decrease in water vapour in the atmosphere downwind; while the introduction of irrigation for agriculture has the opposite effect. Over time, both of these human activities can alter patterns of rainfall, turning deserts into green areas and green areas into deserts.
In other cases the human causes of climate change are more complex. Emissions from cement production, pollution and the release of particulates to form smog in the atmosphere, all affect climate.
Without doubt the most significant of all the human causes of changing climate is the dramatic increase in CO2. After remaining relatively steady for the last 650,000 years or more, in just the last two hundred years the concentration of CO2 in the atmosphere has suddenly shot up from 280, to more than 380 parts per million. And it’s still rising. This dramatic 30% increase has all taken place at the same time as humans have been burning fossil fuels at a greater and greater rate.
Of course there are also natural sources of the CO2 in the atmosphere, such as vegetation, but fortunately there are differences that scientists can measure between the CO2 derived from fossil fuels and the CO2 derived from plants. The changing concentrations of the two types demonstrate that the additional CO2 can only be the result of human activity.
Of course, as CO2 is the most common of greenhouse gasses, the additional concentration is what causes most of the rise in temperature. This is resulting in a change in weather patterns and ocean currents; the melting of global ice formations; and an increase in extreme weather events.
So, yes; though we might be pretty helpless when it comes to controlling the weather, humans are certainly capable of changing the world’s climate.
This post is the Basic version (written by Graham Wayne) of the skeptic argument "Humans are too insignificant to affect climate". We're currently going through the process of writing plain English versions of all the rebuttals to skeptic arguments. It's a big task but many hands make light work. If you're interested in helping with this effort, please contact me.
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What you get is a warming trend stretching back to the start of the record with low frequency oscillations. The most recent 'extreme' warming doesn't even show up as anything out of the ordinary. Tell me how humans have caused this and it is not natural variability?
Humans can change our planet doesn't mean they have changed it in all the ways we think.
The current 390ppm of CO2 simply isn't in the range of natural variations for the last half million years.
On the other hand, we know we're currently adding 29Gtn of CO2 to the air every year (enough for 4ppm increase), of which half seems to be sticking around in the air (2ppm yearly increase), the rest going into sinks like the ocean.
So we would have to disregard our CO2 output and believe that a few Amazons we haven't been tracking have burned/decayed? Or perhaps we can conclude that it's our CO2 output?
As you can see, after 2002 Armagh Observatory is cooling at an alarming rate of 13.2°C/century.
However there are some significant trend divergences from the Armagh data in the pre 20th Century period. It is in this period that there are higher uncertainties. In the 20th Century the 100yr trends are indistinguishable, which casts doubt on claims on some skeptical websites that "Urban Heat Island" (UHI) effects may have affected the Central England record. These same websites suggest Armagh is unaffected by UHI.
Given the above, an eight year gap in the records (filled from Dublin data), and the discussion of uncertainties in the papers, we should be cautious about interpreting data from a single site from the very early instrumental period, though we are lucky to have these precious early instrumental records.
Berényi Péter at 00:23 AM on 28 August, 2010
You state: “For the last 30 years it's +0.21°C/decade. However, for the last 20 years it is only 0.06°C/decade and for the last 80 it's 0.046”
I am not sure how you have generated your values. Here are values I derived from the monthly data up to July 2010. Unless I am mistaken the 20 yr and 30 yr trends are not significantly different.
We also have to factor in the different forcing factors operating at different times, and uncertainties, which are high in the early data, compared with the modern data. Though this will sound a little perverse, a multidecadal slope in the early part of the data may be less statistically significant than a similar slope in the modern data where measurement errors are very small indeed. Anyone pointing to the very early CET temperature variations should bear in mind the Mercury thermometer was invented around 1714, and the Stevenson Screen around 1864. For Armagh, there were some documented 19th century thermometer errors of around 3 degrees Fahrenheit (if memory serves) which was a potential problem when trying to calibrate some of the early data.
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