Global Warming at Home

I checked out the Sydney weather this morning on the SMH Website (as you do on a Monday morning…). The site gives a nice snapshot of the forecast as well as historical statistics. As I cast my eye over the week’s forecast maximum temperatures (24°C, 26°C, 23°C, 21°C, 21°C, 22°C, 22°C) I was pleased by the mild weather. I then noticed the “Average Max” statistic for May: 19.4°C. A quick calc produced an average maximum temperature of 23.7°C for the next seven days! Hardly rigorous scientitific analysis, I admit, but still…

Needing any credible excuse to avoid starting the work week, I went off to Google to find long term temperature statistics for Sydney, which, as you would expect these days, are available on the WWW. Even more impressive, you can get it off the BOM’s “Climate Data Online” website. The oldest official data was recorded at Sydney’s Observatory Hill weather station and dates back to 1859 – only 150 years of data unfortunately. The first land-based observations were made by William Dawes, who arrived with the First Fleet in 1788. He built an observatory at Sydney Cove and for the next three years kept daily records of the wind, temperature, pressure and rainfall, but that’s another story…

Mean Maximum Daytime Temperature, Sydney 1859 to 2009

Mean Maximum Daytime Temperature

I wanted to do a bit more than just look at average maximums for the month, so I downloaded and analysed:

I calculated the mean, maximum and minimum temperatures for winter (May to August) and summer (November to February the following year) and added a trend line to each data set to show the 10-year moving average.

The daily maximum temperatures (lowest and highest for the month) aren’t all that useful, because they really are the outliers and, while the trend may be usefull, the scatter makes interpretation difficult. The monthly mean maximum temperatures shown above are very interesting though, particularly the maximums for winter.

There is no doubt it’s been getting steadily warmer over the last 150 years. The mean winter daytime maximum temperature is probably the most significant indicator and winters are definitely a lot milder now (10 year moving average of 19.2°C) than in the 19th century (16.7°C) . While there is a noticable “kick” upwards in the graph in the last decade, the rate of increase (2.5°C in 150 years or 0.017°C/per annum) appears to have been pretty steady though and I can’t really see an acceleration in the temperature rise during the past three of four decades (when greenhouse gas emissions were meant to have become the main contributing factor). In fact, if Sydney-siders had been paying attention to the climate instead of worrying about the Great Depression and WW1, they’d have been pretty anxious about the temperature increase during the period 1901 to 1927, when 10-year moving average maximum temperatures in winter increased by 2.3°C, from 16.0°C to 18.3°C.

Southport – Sydney, 20/09/2008

We’re still flying along, making 9 to 10 knots SoG (speed over the ground) on average. The current is between 2.5 and 3 knots behind us, 20 miles offshore!

I decided to put the kite up this morning. What a drama! Sarah, Vicky and George had packed it beautifully with rubber bands in July, and it went up just perfectly. We sheeted on, the rubber bands snapped and we were flying. All good, until Sebastian inadvertently disengaged the Autohelm… Got it wrapped round the forestay then got knocked flat just as Sebastian and Bobby got it untangled. Threw the after guy off and just blew it off…

With the genoa set I ordered the kite re-packed, complete with rubber bands. This time I stood on the helm while they popped it. Sheet on and suddenly I have bucking wild animal in my hands! She’s surfing at 11 knots boat speed! That’s 4 knots over hull speed! I managed half an hour of this before terror overcame exhiliration… Blew her off, hauled the kite in, set the poled out genoa again and Bobby and Sebastian packed the kite like pros this time!

Flying kites takes concentration!

Southport – Sydney, 19/09/2008

If you have to sail from Southport to Sydney, and you’re in a hurry, what would you wish for: 25 knot northerlies and a 3 knot current behind you? That’s exactly what we’ve got! In just over 10 hours since leaving the Gold Coast Seaway we’ve done 90 miles directly towards our target: Broken Bay, Sydney. At this rate we’ll do the 400 mile trip in less than 48 hours, even allowing for loss of the current around Port Macquarie!

Proof of progress, 9 knot ground speed and 90 miles at 5:30PM...