Meteorology question!?

Question

Can Anyone help me out on this question?

How is the length of a temperature record related to our ability to deduce the existence of an underlying upward trend(due, for example, to increasing greenhouse gases)?

simple one phrase or short sentence is good. thanks

Answer 1

You might deduce that if a warms spell is last for a few days longer than normal that it is an indication of climate change and warming but that isn't true.  It is a cycle and seasonal temperatures are not a good way to predict that.

Answer 2

If you have say hourly temperatures for a day, all you know is the trend for the day. If you have a decade of daily maximum temperatures, then you can say something about the trend during that decade... and so on.

In reality, though, because of changing temperature measurement technologies, observation practice, thermometer screen design, site changes, environment changes (ground type, trees growing nearby, or being cut down), surrounding environment (growth of urban areas, change of land use) it is pretty hard to find a long temperature record where "everything else is equal" and any trend is only the underlying climate.