Geography discussion 1

Arctic Climate Change

The difference during summer is increasing as the sea ice extension is decreasing in

relation to the recent past.

http://nsidc.org/arcticseaicenews/

In lecture 1, we learned about the seasonal migration of Arctic sea ice extension. In this figure, it is very clear that 2012 was exceptional because the Arctic sea ice during that summer was at the greatest minimum ever observed, dropping far below the mean of the long term trend. Let’s take a look what happened after, particularly in 2016.

(National Snow and Ice Data Center)

This figure is based on a report of sea ice extension in November 2016. At the end of summer in 2016, the minimum sea ice extension was the second lowest after the 2012 extension (left red arrow). As the season migrates and turns colder, the sea ice did not grow back as fast as it should have relative to all previously measured patterns (right red arrow). By November, the sea ice extension was the lowest ever recorded in November.

What was happening in 2016?

Daily mean temperatures for the Arctic area north of the 80th northern parallel. (Danish Meteorological Institute)

Arctic temperatures are about 20 degrees Celsius higher than normal above 80 degrees North Latitude! (Nov 2016).

This figure shows daily temperature measurements in the Arctic at 80 degrees north in 2016 (red line) along with a computer simulation of temperature patterns based on long- term temperature measurements of the Arctic region (green line). The blue line is the point of freezing (0 degree Celsius). Please note that Y-axis identifies temperature shown in units Kelvin (K). Kelvin is a commonly used unit of measurement in science for temperature. Please see the following slide for more detail. The X-axis identifies the number of days in 2016. For example, the day 1 indicates January 1st, and the day 365 equates to December 31st.

As you can see, there is seasonal variation. You will also notice that, most of the year, the temperature remains below the freezing level (blue line), although it will slightly exceed freezing for a short period of time during summer. In November of 2016, the temperature north of 80 degrees latitude was around -5 degrees C. This is below freezing (not by much), but is anomalous to the normal temperature of around -25 degrees C (see vertical blue dashed line). The temperature difference between the long term mean (green line) and the observed temperature (red line) was as great as 20 degrees!!

(continue)

(continued) Why was this happening? Why did it happen in the Arctic? This phenomenon is known as polar amplification and it is important that we learn about this concept to understand how and why changes in our climate system affect different parts of the world unequally. For now, maintain an awareness of polar amplification as we will learn more about this concept in the following weeks.

In the meantime, please take a moment to think about whether such daily temperature changes north of 80 degrees latitude are considered “climate” or “weather”?

Further, please check the latest news from Arctic Sea Ice News and Analysis for additional information: https://nsidc.org/arcticseaicenews/

A recent science study reports that rapid warming in the Arctic is a likely driver of the recent extreme winter weather in the US. https://www.science.org/doi/10.11 26/science.abi9167?utm_campaign =SciMag&utm_source=Social&utm_ medium=Twitter

Fahrenheit is a temperature scale based on one proposed in 1724 by the German physicist Daniel Gabriel Fahrenheit. 0 F was the lowest temperature Dr. Fahrenheit could measure, 100 F is the average human core body temperature. In scientific measurement, Kelvin is more common because by definition 0 Kelvin is called absolute zero. Absolute zero is theoretically the lowest possible temperature where all molecules seize their motion (almost no heat is emitted by the molecule). In this slide, temperatures in Fahrenheit, Kelvin, and Celsius are compared in the same scale.

Weather Forecasting

• Weather affects nearly everyone, every day.

• Weather forecasts are issued: o To save lives o Reduce property damage o Reduce crop damage o To let the general public know what to expect

• Forecasts are often utilized to make many important decisions on a daily basis

• So how is it done, and how is it done correctly?

National Weather Service Mission:

• The NWS provides weather, hydrologic, and climate forecasts and warnings for the US, its territories, adjacent waters, and ocean areas for the protection of life and property and the enhancement of the national economy.

Tools available to a forecaster…

• Weather Observations (including surface data, satellite data, and radar data)

• Commercial aircraft data

• Wind profilers

• Numerical Model Output

…There are a lot of sources for data!

Forecasting technique - Persistence

13Image from WW2010 Online Guide

The most primitive method of forecasting is to observe and estimate that there will be no changes to the present. Today is sunny, therefore, tomorrow will also be sunny. This may work relatively well in a dry and arid region, but does it work in the New England region? Probably not.

The Trend Technique

15Image from Meteorology Today by C. Donald Ahrens

Another method of forecasting that has been used in the more recent past is to understand trends. As we all know, however, weather systems migrate from west to east in the mid latitude, where we live, due to prevailing wind called the westerly (we will cover this in the following weeks). The atmospheric pressure system, in general, crosses over North America in 3 to 5 days. With this, the system travels approximately 800 miles per day. With this understanding, we can broadly predict when a storm will approach a specified region. Can this be used to make an accurate prediction? Although this maybe not be a desirable way to forecast for a long-term period, it may work for a shorter and current time interval.

The Analogue Technique

17

The analogue technique is a combination of climate and weather. Based on long- term observations, you might be able to identify a clear pattern in the atmospheric system. For instance, you may notice that, statistically, when a dry and cold weather pattern is observed in the northwest (high pressure system), there is a tendency for stormy weather in the northeast (low pressure system). This method could be useful and may produce relatively reliable results for slightly longer time periods (few days to a week).

Accuracy and skill in forecasting After you learn about forecasting techniques, you may be asking yourself

– what is an ”accurate” forecast?

• What is an accurate forecast? o Your forecast for tonight’s minimum temp is 0F

If the actual minimum was 1F, is it inaccurate?? If the actual minimum was 10F, is it inaccurate??

o Accuracy (in forecasting) is arbitrary and relative – it is not clearly or objectively defined.

19

Modern weather forecasts are based on model forecasts

– Numerical Weather Prediction In order to increase accuracy, we heavily rely on numerical weather prediction.

• Predict the state of the atmosphere (e.g., pressure, temperature, precip, winds, etc) in time

• Use mathematical equations – initialized with observational data

…Why are models often wrong?

20

Problems with numerical modeling

21

• Models represent a “simplified” atmosphere – not every real process in atmosphere can be resolved in models.

• Many are not global in coverage

• The initial atmospheric state is not well-known

• The data may also have errors in it

• The model equations compute quantities at grid points (30- 50km).

• The atmosphere is fundamentally chaotic!

So, the atmosphere is fundamentally chaotic and this is why weather forecasting, although state of the art, is still not perfect. Therefore, in order to understand the climate system, scientists focus on key phenomena and/or relationships that effectively control or alter the climate system of the Earth. Here, we call them the “climate knobs” and let’s talk more about it in the next lecture.

Here is a news from weather forecast development:

Artificial Intelligence May Be Key to Better Weather Forecasts Recent advances in machine learning hold great potential for converting a deluge of data into weather forecasts that are fast, accurate, and detailed. By Sid-Ahmed Boukabara, Vladimir Krasnopolsky, Jebb Q. Stewart, Stephen G. Penny, Ross N. Hoffman, and Eric Maddy, 1 August 2019

https://eos.org/opinions/artificial-intelligence-may-be-key-to-better-weather-forecasts

https://www.ncdc.noaa.gov/billions/overview

“In 2021, there were 20 weather/climate disaster events with losses exceeding $1 billion each to affect the United States.” “Overall, these events resulted in the deaths of 688 people and had significant economic effects on the areas impacted.”

https://www.noaa.gov/news/2021-was-worlds-6th- warmest-year-on-record

2021 was world’s 6th-warmest year says NOAA

https://medialibrary.climatecentral.org/resources/2020-in-review-global-temperature-rankings

– Could we have predicted that 2021 would become the 6nd warmest year on record or predict what 2022 temperatures will look like when the report becomes available? The answer is no. However, you can look into the long-term trend and anticipate what likely will happen in the future! (weather vs climate)

Please take a moment to read the article published in March 2017 about our perceptions of climate change. This was before the catastrophes caused by Hurricane Harvey and Hurricane Irma in 2017.

How Americans Think About Climate Change, in Six Maps

By NADJA POPOVICH, JOHN SCHWARTZ and TATIANA SCHLOSSBERG

MARCH 21, 2017 https://www.nytimes.com/interactive/201 7/03/21/climate/how-americans-think- about-climate-change-in-six-maps.html

Example Test 1 question: Climate differs from weather in that

A. climate is a broad composite of temperature conditions, while weather addresses temperature as well as precipitation, snow and ice cover, and wind conditions.

B. climate change occurs over longer durations than do weather changes.

C. climate change is exclusively global, whereas weather is exclusively regional.

D. climate and weather do not differ, they are interchangeable terms.

At last, here is an example questions in preparation for the test. The questions in test 1 will be similar in format to this question, but not necessarily the same question.

The answer is B.