Ice core measurements give you a value for each year. You’re looking for changes in the ice that are driven by yearly seasonal changes, notably the periods of summer where the ice received 24hour of sun for weeks.
It’s perfectly reasonable to take daily measurements, average them into yearly measurements. Then compare them to yearly averages taken from ice cores.
The only reason we can even use ice cores for temperature measurements is because they’re have high enough resolution that we’ve been able to observe the impact of global temperature on the most recent layers of ice. It’s not like someone drilled an ice core one day and discovered a bunch of temperatures sharpied down the side. They drilled many ice cores, then spent months correlating observed patterns to temperature records so they could build a model that allows them to understand the link between temperature and observed patterns in the ice.
Don’t mistake a record measuring thousands of years of history for a record that only records every thousand years.
Thes resolution is yearly going back only about 2000 years. Everything beyond that, the resolution is much lower. Where is that data from and don't you see how much "smoother" it is?
Your link has a citation leading to the source article. I would recommend you read it if you’re interested (use Scihub if you need to).
The thrust of the underlying article is looking at the exact question you’re asking, can ancient ice records that have a more limited resolution of 20-500 years be compared to centennial or millennial scale data, and can you draw useful conclusions about time periods of that range.
Thank you for pointing that out, it was a fascinating read. I did observe that they said "essen-tially no variability preserved at periods shorter
than 300 years" which seems to imply that drawing a conclusion between their older data and the recent data could be perilous when looking at periods shorter than that (e.g. last 100 years)
It’s perfectly reasonable to take daily measurements, average them into yearly measurements. Then compare them to yearly averages taken from ice cores.
The only reason we can even use ice cores for temperature measurements is because they’re have high enough resolution that we’ve been able to observe the impact of global temperature on the most recent layers of ice. It’s not like someone drilled an ice core one day and discovered a bunch of temperatures sharpied down the side. They drilled many ice cores, then spent months correlating observed patterns to temperature records so they could build a model that allows them to understand the link between temperature and observed patterns in the ice.
Don’t mistake a record measuring thousands of years of history for a record that only records every thousand years.