Sea Level Trend 1850-2024

Abstract

This work describes the determination process of the sea level dataset in 1850-2024. Data for 1880-2024 are based on measurements, and for 1850-1880, on the parabolic trendline. The original data are according to various baselines and were converted in this work to the uniform "pre-industrial" 1850-1900 baseline. In 2024 the global sea level was 258 mm above the 1850-1900 baseline. The average sea level change in 1994-2024 was 3.33 mm/y. The acceleration of the sea level rise is currently 0.0164 mm/y 2 , (0.0164 mm/year)/year. The sea level change per 1°C of global warming decreased from 265 mm/°C in 1980 to 197 mm/°C in 2020. The dataset is available on the website nowagreen.com.

Full text

Sea Level Trend 1850-2024
Joseph Nowarski, M.Sc., ME – Energy Conservation Expert
Version 1.1.1, 20 February 2025
DOI:10.5281/zenodo.14899702
all versions DOI:10.5281/zenodo.14899584
Abstract
This work describes the determination process of the sea level dataset in 1850-2024.
Data for 1880-2024 are based on measurements, and for 1850-1880, on the
parabolic trendline.
The original data are according to various baselines and were converted in this
work to the uniform “pre-industrial” 1850-1900 baseline.
In 2024 the global sea level was 258 mm above the 1850-1900 baseline.
The average sea level change in 1994-2024 was 3.33 mm/y.
The acceleration of the sea level rise is currently 0.0164 mm/y2, (0.0164
mm/year)/year.
The sea level change per 1°C of global warming decreased from 265 mm/°C in
1980 to 197 mm/°C in 2020.
The dataset is available on the website nowagreen.com.

Sea Level Trend – Joseph Nowarski
2/9
Glossary
Ave Average
BL baseline of surface temperature change (GW),
pre-industrial = 1850-1900
CF Conversion Factor across baselines
GW Global Warming, global surface temperature above the 1850-1900
baseline, land+ocean, °C
SL sea level above the pre-industrial 1850-1900 baseline, mm
SL/GW sea level change per 1°C of global warming, the ratio of sea level
change (SL) above the 1850-1900 baseline to the global warming
(GW) above the same baseline, mm/°C
TL trendline
Global Warming Baseline
All global warming and climate change results of calculations in this work are
above the pre-industrial 1850-1900 baseline, °C.
Data Sources
Data sources for sea level trend
o NOAA [1]
o NASA [2]

Sea Level Trend – Joseph Nowarski
3/9
Table 1 - Database for sea level trend
NOAA NASA
Reference [1] [2]
Units mm mm
Records quarterly 14 days
Selected Jun-Aug middle of each year
From 1880 1993
To 2024 2024
Years 145 32
Baseline (BL) 1993-2008 1996-2016
BL years 16 21
Decimal places 2 2
Ave in BL 1.94 0.28
Sea Level Change
NOAA sea level dataset [1] is above the 1993-2008 baseline.
Chart 1 - Change in sea level, mm above 1993-2008 baseline [1]
y = 0.008564888898x
2
- 0.047639747200x - 177.512387360629
-250
-200
-150
-100
-50
0
50
100
150
1850
1860
1870
1880
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
2020
The current work applies the pre-industrial 1850-1900 baseline to all datasets.
However, the sea level dataset starts in 1880, after 1850.
To convert the sea level dataset to the 1850-1900 baseline, data is required for the
1850-1880 period. The missing data may be calculated using the parabolic
trendline.

Sea Level Trend – Joseph Nowarski
4/9
Table 2 - Parabolic trendline of sea level change 1880-2024 above the 1993-2008
baseline
a 0.008564888898
b -0.047639747200
c -177.512387360629
Start 1849
Conversion Factor to 1850-1900 Baseline
The conversion factor for the NOAA [1] dataset from the 1993-2008 baseline is
+172.33 mm and for the NASA [2] dataset from the 1996-2016 baseline +195.48 mm.
NOAA and NASA Data Converted to 1850-1900 Baseline
Chart 2 - NOAA [1] and NASA [2] data converted to 1850-1900 baseline, mm
-50
0
50
100
150
200
250
300
1850
1860
1870
1880
1890
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
2020
NOAA NASA

Sea Level Trend – Joseph Nowarski
5/9
Chart 3 - NOAA and NASA sea level combined data above 1850-1900 baseline,
mm
140
150
160
170
180
190
200
210
220
230
240
250
260
270
1993
1995
1997
1999
2001
2003
2005
2007
2009
2011
2013
2015
2017
2019
2021
2023
NOAA NASA NOAA+NASA
Corrected Parabolic Trendline
Conversion of the NOAA and NASA datasets to the uniform 1850-1900 baseline
allows correction of the initial estimation of the 1850-1880 data.
Table 3 - Parabolic trendline of sea level change 1880-2024 above the 1850-1900
baseline
a 0.008203454995
b 0.511879017401
c 0.216920586719
Start 1879
This trendline is applied for the correction of 1850-1880 data.
Sea Level Trend Dataset on Website
The sea level dataset is available on site nowagreen.com [4].

Sea Level Trend – Joseph Nowarski
6/9
Sea Level Average Change
The average sea level change in 1994-2024 was 3.33 mm/y.
Acceleration of the Sea Level Rise
The parabolic trendline of the sea level is:
SL = a*y2 + b*y + c
SL sea level above the pre-industrial 1850-1900 baseline, mm
y year
a, b, c trendline coefficients as in Table 3
First-order derivative:
bay
dy
SLd  2
)(
Second-order derivative:
a
dy
SLd 2
)(
2
2

The acceleration of the trendline is the second-order derivative of the parabolic
trendline.
As calculated from the trendline in Table 3, the acceleration of the sea level rise is
0.0164 mm/y2, (0.0164 mm/year)/year.

Sea Level Trend – Joseph Nowarski
7/9
Sea Level Change per 1°C of Global Warming
Chart 4 - Sea level change per 1°C of Global Warming, actual data, mm/°C
y = 0.025209924601x
2
- 2.770626099025x + 267.900935497441
150
170
190
210
230
250
270
290
310
330
350
1980
1990
2000
2010
2020
Considering the 1980-2021 parabolic trendline, the SL/GW parameter changed
from 265 mm/°C in 1980 to 197 mm/°C in 2020.

Sea Level Trend – Joseph Nowarski
8/9
Chart 5 - Sea level change per 1°C of Global Warming considering parabolic
trendlines 1910-2021, mm/°C
150
200
250
300
350
400
450
500
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
2020
According to the above chart based on SL and GW trendlines, the SL/GW
parameter changed from 463 mm/°C in 1923 to 258 mm/°C in 1980 and 198
mm/°C in 2021, showing a small difference from the previous chart based on
actual data.
According to both charts, the SL/GW parameter is currently decreasing.

Sea Level Trend – Joseph Nowarski
9/9
References
1. Climate Change: Global Sea Level - NOAA
https://www.climate.gov
2. Global Mean Sea Level Data – NASA - GSFC. 2024. Global Mean Sea Level
Trend from Integrated Multi-Mission Ocean Altimeters TOPEX/Poseidon,
DOI:10.5067/GMSLM-TJ152
https://sealevel.nasa.gov
3. Global Surface Temperature Changes Datasets Converted to 1850-1900
Baseline v1.1.2 – Joseph Nowarski, DOI:10.5281/zenodo.6461153
4. NowaGreen Global Warming Database - Sea Level Trend, mm above 1850-
1900 Baseline
https://nowagreen.com/sl.php
* * *