Those in denial of global warming and its danger have tried to make a big fuss over what they perceive as a lack of warming recently. How recently depends on just how much they’re willing avoid seeing.
Time and time again we’ve explained that natural variations can mask a trend on short time scales, and the time scales used to deny the danger of climate change are short. Time and time again we’ve illustrated that certain known factors (like the el Nino southern oscillation) have acted to do just that. For those in denial, any such explanation falls on deaf ears. But for the sake of those who are honestly wondering, let’s take a look at what climate data have revealed very recently. In particular, let’s look at the last decade (plus a couple of months) — let’s see what has happened since the start of 2003.
Such a short time span should be a denier’s dream! Ordinarily we wouldn’t expect to find significant climate-related changes over such a brief period. The usual definition of climate is the average and variation of weather over long periods of time, with “long” typically referring to at least 30 years. With only a third of that much time, it would be genuinely alarming to find multiple indicators of significant change. Even if global warming continues apace, we could well still find nothing notable at all. Ten years is just too little time.
Yet some parts of the earth are screaming so loudly that not even limiting time to ten years can drown out the message. Perhaps best-known is the sea ice in the Arctic. Its extent has declined so fast that even the last 10 years show a significant trend (because the annual cycle has changed so strongly, anomalies are computed using “since 2003″ as a baseline):
If we focus on the month of September when Arctic sea ice reaches its annual seasonal minimum, we find a truly astounding result: a statistically significant downtrend in spite of only 10 years and a mere 10 data points:
As remarkable as that is, we find even more significant decline in sea ice volume rather than extent:
The annual seasonal minimum of sea ice volume has almost dropped off the face of the earth, reducing by 68% in just the last decade:
Even with just a decade of data, the changes we have wrought are evident.
One decade is also more than enough to see the continued change in sea level:
Despite the mistaken claims of some, the rate of sea level rise in this all-too-brief period is significantly higher than its average rate during the last century.
Sea level rise is principally for two reasons. First, the melting of land ice moves water from land to sea. Second, heating of the oceans themselves causes them to expand.
Speaking of ocean heating, we can see a significant trend in just 10 years of ocean heat content down to a depth of 700 meters:
The trend is even stronger (both in its size and its statistical significance) in a mere 8 years of data for ocean heat content to a depth of 2000 meters:
Data for northern hemisphere snow cover anomaly shows a slight decline since 2003, but it’s not statistically significant:
Looking at individual seasons, however, one season does show a statistically significant trend: summer (June-July-August). And it’s a whopper:
Summer 2012 had, on average, 42% less snow cover than summer 2003.
None of the five main global temperature data sets shows statistically significant trend since 2003. But if they’re adjusted to remove the influence of known extraneous factors — el Nino, aerosols, and solar variation — there is one which does show a statistically significant trend despite being limited to a mere ten years and two months. That’s the lower-troposphere data from UAH:
Its estimated trend since 2003 is 0.018 deg.C/yr, even higher than its estimated trend since these data begin in December 1978.
The plain truth is that in spite of using far too little time, the impact of man-made climate change is still clearly imprinted on the data. And that goes for the last decade, not just the decades preceding it.
The pity is that we have precious little time to take effective action to mitigate future changes. Too little time.