Note that their claim is AVERAGE temperature, over all 4.1C above "normal".
Well, first, what is "normal"? They are using anything that is above or below the baseline as being "abnormal", the baseline being normal. This is false. What is "normal" is values within one standard deviation above and below the average.
So is this spring the "warmest", above normal, on record?
The problem one has when using the spring or fall to show a long term trend is those two seasons are transitions. That means, for spring the temperature will be rising as we move from winter to summer. There will be a slope to that rise in temperature. That slope is the rate at which we change from the winter temps to the summer temps.
So let's have a look at that for Station 4333, Ottawa Airport. This is the full range of daily temps for spring 2010 (March 1 to May 31).
Notice the early part of April with that spike (down then up), and the middle of May. Some may recall that heat wave we had for a couple days. As a side note, total wind output during that period was less than 5% of name plate capacity. Right when we had that spring heat wave, wind produced virtually nothing.
So how does this compare to previous years? Recall they are claiming this is the warmest spring since 1946. So let's see if it is. Using only max temps for all years, this is the range of temps for those three months: The top red line is the highest daily maximum temperature for all years 1900-2009. The bottom blue line is the lowest of the daily maximum temperature for all years 1900-2009. The orange is the upper and lower standard deviation, and the grey line is the average for those years. The thick black line is 2010.
You will note that 2010 is well within that range, with 3 days of exceptions. You will also note that 2010 went into March warmer than the upper standard deviation, but the end days of spring are around the upper standard deviation. This will tend to shallow the slope of the trend for 2010 compared to other years.
This can be seen when plotting the slopes for all years.
This graph takes all the days for each year and plots the slopes of the max temps for each year. The value of the slope can be from several factors. A steep slope, with a larger number, means that within those 92 days the temperature change increased more so than a shallow slope. A steep slope can also mean a rapid onset of summer. A shallow slope could be one of two things, it took longer for summer to arrive in that period, or the winter was warmer and there was less change in temp needed to get to summer.
You can see from this graph that over time, the slope, the rate at which summer came to be, has been dropping. 2010 is one of the shallowest slopes, only beaten by previous 3 years since 1900. This makes perfect sense since we know that summers have not increased in temps since 1900 but the winters have been less cold. Thus the transition from winter to summer has less to travel. Doesn't mean the spring is "warmer", just less transition needed to get to summer. It was winter that was warmer, not the spring transition.
Notice 1900 was quite steep, one of the steepest (starting from a colder winter). So let's see the max temps for those two years and the linear trends for both:
It is very clear that 2010 went into the spring warmer than 1900, 10C warmer, but by the time April and May came, the two are nearly the same.
So claiming 2010 was the "warmest" since 1946 is a crock, a clear misrepresentation due to omission of detailed data. 2010 was "warmer" only because we went into spring from a warmer winter.
The question to ask is why did EC portray spring in this way? Why leave out crucial details that shows what actually happened?
I will do other stations, and an over all for the country in another posting. One does wonder how their map was derived when there are places in Canada that do not gather any data. Part of the "extrapolation" climate scientists do. In other words, inventing data where none exists.