Artic Sea Ice Extent

The chart above is from the book Data At Work by Jorge Camoes. In this article we try to recreate the chart from Chapter 13 - Profiling, that displays the extent of Artic and Antartic sea ice from 1978-2015. We will use the Altair charting library.

import pandas as pd
import numpy as np
from pathlib import Path
import ipywidgets as widgets
import calendar
import altair as alt

Sea Ice Data Files

root=Path('../data/seaice')

month_files = [str(f) for f in root.glob('*.csv')]

A function to load data for each month

def load_month(index):
    month_file = month_files[index]
    df = pd.read_csv(month_file, dtype={'year': str})
    df.columns = [col.strip() for col in df.columns]
    df = df.replace(-9999.0, np.nan).replace('-9999', np.nan)
    df = df.fillna(method='ffill')
    return df

monthly_ice = {i : load_month(i) for i in range(len(month_files))}

Create the Sea Ice Extent Chart

height=140
width=100

def ice_chart(month, col='extent'):
    return alt.Chart(monthly_ice[month]).mark_line().encode(
        x=alt.X('year:T', 
                axis=alt.Axis(title='')),
        y=alt.Y(f'{col}:Q', 
                scale=alt.Scale(domain=(3, 18)),
                axis=alt.Axis(title=''))
    ).properties( height=height,
                  width=width,
                  title=f'{calendar.month_name[month +1]}'
        )

def ice_charts(col='extent'):
    first_half = ice_chart(0, col) | ice_chart(1, col) | ice_chart(2, col) \
                | ice_chart(3, col) | ice_chart(4, col) | ice_chart(5, col)
    second_half = ice_chart(6, col) | ice_chart(7, col) | ice_chart(8, col) \
                | ice_chart(9, col) | ice_chart(10, col) | ice_chart(11, col)

    return alt.vconcat(first_half, 
                second_half
               ).properties(
                 title=f'Monthly Sea Ice {col.title()} 1978-2020 million km\u00B2'
            )

Monthly Artic Sea Ice Extent

After creating the ice_charts function we can now use it to display the charts.

ice_charts()

Monthly Sea Ice Area

ice_charts('area')